The structural, electronic and magnetic properties of Fe7S8 material have been studied within the framework of the ab-initio calculations, the mean field approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin σ=5/2 are the most probable configurations. A mixed Ising model with ferromagnetic spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has been used to study the magnetic properties of this compound. We demonstrated that the magnetic phase transition can be either of the first or of the second order, depending on the value of the exchange interaction and crystal field. The presence of vacancies in every second iron layer leads to incomplete cancellation of magnetic moments, hence to the emergence of the ferrimagnetism. Anomalies in the magnetization behavior have been found and compared with the experimental results.
Magnetic properties of the intermetallic compound NdCo$_2$Si$_2$ are investigated by using the Monte Carlo simulation (MCs) under Metropolis algorithm. The magnetism of the compound is caused by the existence of the rare earth (Nd3+) ions with a magnetic moment taking the value 2.7 muB. Firstly, the ground state phase diagrams are presented and discussed in different planes corresponding to different physical parameters of the system. The stable phases are explored for different configurations of the Hamiltonian of the system. These stable phases are determined by the minimal energies. For non…
The aim of this paper is to investigate the magnetic properties of the M_n B_i magnetic systems by using the Monte Carlo simulation. Indeed, we analyzed the effect of the number of layers on the magnetic properties of the compound M_n B_i. The magnetization, the binder cumulant, the Curie temperature and the hysteresis cycle are also calculated in this work. We used the free boundary conditions to simulate the properties of the studied system, and we presented the effect of multilayer numbers on the magnetic properties of M_n B_i films. Meanwhile, there are clear indications that coercive fiel…
In this work, a study of the magnetic behavior of the spinel ZnFe2O4 is presented by using the Monte Carlo simulations (MCS). The iron atoms provide the magnetism in this material. In fact, the magnetic spin of moment of the Fe3+ ions is S=5/2. In this context, we propose a Hamiltonian describing and modeling this compound. Firstly, at zero temperature we have studied the ground state phase diagrams of the system in order to find the more stable configurations. On the other hand, for a non-null temperature values, we obtained the results of the Monte Carlo simulations, namely: the magnetizatio…
Using Density Functional Theory and a thermodynamic model [Physical Review B 86, 134418 (2012)], in this paper, we provide an approach to systematically screen compounds of a given Heusler family to predict ones that can yield giant magnetocaloric effect driven by a first-order magneto-structural transition. We apply this approach to two Heusler series Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at Ni and Mn sites. We predict four new compounds with potentials to achieve the target properties. Our computation…
Spinel structured compounds, $AB_2O_4$, are special because of their exotic multiferroic properties. In $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$), a switchable polarization has been observed experimentally due to a non-collinear magnetic spin order. In this article, we demonstrated the microscopic origin behind such magnetic spin order, hysteresis, polarisation and the so-called magnetic compensation effect in $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$, $Ni$) using Monte Carlo simulation. With a careful choice of the exchange interaction, we were able to explain various experimental findings such as magnetization…
By analogy with Monte Carlo algorithms, we propose new strategies for design and redesign of small molecule libraries in high-throughput experimentation, or combinatorial chemistry. Several Monte Carlo methods are examined, including Metropolis, three types of biased schemes, and composite moves that include swapping or parallel tempering. Among them, the biased Monte Carlo schemes exhibit particularly high efficiency in locating optimal compounds. The Monte Carlo strategies are compared to a genetic algorithm approach. Although the best compounds identified by the genetic algorithm are compar…
Accurately predicting the formation energy of a compound, which describes its thermodynamic stability, is a key challenge in materials physics. Here, we employ many-body quantum Monte Carlo (QMC) with single-reference trial functions to compute the formation energy of two electronically disparate compounds, the intermetallic VPt$_2$ and the semiconductor CuI, for which standard density functional theory (DFT) predictions using both the Perdew-Burke Ernzerhof (PBE) and the strongly constrained and appropriately normed (SCAN) density functional approximations deviate markedly from available expe…
The structural and magnetic anomaly of the layered compound SrFeO$_{2}$ were examined by first principles density functional calculations and Monte Carlo simulations. The down-spin Fe 3$d$ electron occupies the $d_{z^2}$ level rather than the degenerate ($d_{xz}$, $d_{yz}$) levels, which explains the absence of Jahn-Teller instability, the easy ab-plane magnetic anisotropy and the observed three-dimensional (0.5, 0.5, 0.5) antiferromagnetic order. Monte Carlo simulations show that the strong inter-layer spin exchange is essential for the high Néel temperature.
Using Monte Carlo Simulations (MCS), based the Metropolis algorithm, we examine in this study, the magnetic properties of the rare earth based compound GdN. In a first step, we discuss and study the ground state phase diagrams explored in the different planes of physical parameter. The obtained stable configurations are illustrated by comparing the energies modeled by the Hamiltonian of Eq. (1). For non-null temperature values, we present and discuss the behavior the total magnetizations and susceptibilities as a function of: the temperature, the crystal field, the exchange coupling interactio…
It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting plateaus in the magnetization as a function of the magnetic field at low temperatures. The origin of them is still controversial. In this paper we study the thermal behavior of this compound with a single-flip Monte Carlo simulation on a triangular lattice and demonstrate the decisive influence of metastable states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We consider the [Co2O6]n chains as giant magnetic moments described by large Ising spins on planar clusters with open boundary conditions. With t…
A spin model of LiCu2O2 compound with ground state of ellipsoidal helical structure has been adopted. Taking into account the interchain coupling and exchange anisotropy, we focus on the magnetoelectric properties in a rotating magnetic field and perform the Monte Carlo simulation on a two-dimensional lattice. A prominent anisotropic response is observed in the magnetization and polarization curves, qualitatively coinciding with the behaviors that detected in the experiment. In addition, the influences of the magnetic field with various magnitudes are also explored and analyzed in detail. As t…
In this work, we study the equiatomic quaternary Heusler Alloy CoFeCrP using two methods: DFT and Monte Carlo simulations. The DFT method allowed us to illustrate the structural, electronic and magnetic properties of this alloy. The ground state phase diagrams have been presented to show the stable configurations in different physical parameter planes. On the other hand, the Monte Carlo simulations, performed under the Metropolis algorithm, permitted to deduce the critical the behavior of the equiatomic quaternary Heusler alloy CoFeCrP. The structural properties results show that the phase of …
The simulation scheme for heterostructural growth of compound semiconductors is presented based on the kinetic Monte Carlo method. The sheme is designed as simple as possible in order to apply it for any heteroepitaxial growth on GaAs(001) substrate. The parameters used in the simulation are determined with the first-principles calculation to reproduce experimental RHEED intensity curves for homoepitaxial growth of GaAs(001).
We perform constant pressure Monte Carlo simulations of a spin-analogous model which describes coupled spatial and magnetic degrees of freedom on an fcc lattice. Our calculations qualitatively reproduce magnetovolume effects observed in some rare earth manganese compounds, especially in the anti-Invar material YMn2. These are a sudden collapse of the magnetic moment which is connected with a huge volume change, and a largely enhanced thermal expansion coefficient.
Despite their structural similarities, SrBi$_2$Ta$_2$O$_9$ (SBT) and SrBi$_2$Nb$_2$O$_9$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the Niobium compound the intermediate phase is suppressed and a single transition between the high- and low temperature structures is observed. We present \emph{ab initio} calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize …
We perform a computational screening for two-dimensional magnetic materials based on experimental bulk compounds present in the Inorganic Crystal Structure Database and Crystallography Open Database. A recently proposed geometric descriptor is used to extract materials that are exfoliable into two-dimensional derivatives and we find 85 ferromagnetic and 61 anti-ferromagnetic materials for which we obtain magnetic exchange and anisotropy parameters using density functional theory. For the easy-axis ferromagnetic insulators we calculate the Curie temperature based on classical Monte Carlo simula…
The temperature dependent stability of the magnetic phases of FeRh were investigated by means of total energy calculations with magnetic disorder treated within the uncompensated disordered local moment (uDLM) approach. In addition, Monte Carlo simulations based on the extended Heisenberg model have been performed, using exchange coupling parameters obtained rom first principles. The crucial role and interplay of two factors in the metamagnetic transition in FeRh has been revealed, namely the dependence of the Fe-Fe exchange coupling parameters on the temperature-governed degree of magnetic di…
Mn_5Ge_3C_x films with x>0.5 were experimentally shown to exhibit a strongly enhanced Curie temperature T_C compared to Mn_5Ge_3. In this letter we present the results of our first principles calculations within Green's function approach, focusing on the effect of carbon doping on the electronic and magnetic properties of the Mn_5Ge_3. The calculated exchange coupling constants revealed an enhancement of the ferromagnetic Mn-Mn interactions mediated by carbon. The essentially increased T_C in Mn_5Ge_3C is well reproduced in our Monte Carlo simulations and together with the decrease of the tota…
We present a unified model of compound semiconductor growth based on kinetic Monte Carlo simulations in tandem with new experimental results that can describe and predict the mechanisms for the formation of various types of nanostructures observed during droplet epitaxy. The crucial features of the model include the explicit and independent representation of atoms with different species and the ability to treat solid and liquid phases independently. Using this model, we examine nanostructural evolution in droplet epitaxy. The model faithfully captures several of the experimentally observed str…
A generic method to estimate the relative feasibility of formation of high entropy compounds in a single phase, directly from first principles, is developed. As a first step, the relative formation abilities of 56 multi-component, AO, oxides were evaluated. These were constructed from 5 cation combinations chosen from A={Ca, Co, Cu, Fe, Mg, Mn, Ni, Zn}. Candidates for multi-component oxides are predicted from descriptors related to the enthalpy and configurational entropy obtained from the mixing enthalpies of two component oxides. The utility of this approach is evaluated by comparing the pre…
Density-functional theory is widely used to predict the physical properties of materials. However, it usually fails for strongly correlated materials. A popular solution is to use the Hubbard corrections to treat strongly correlated electronic states. Unfortunately, the exact values of the Hubbard $U$ and $J$ parameters are initially unknown, and they can vary from one material to another. In this semi-empirical study, we explore the $U$ and $J$ parameter space of a group of iron-based compounds to simultaneously improve the prediction of physical properties (volume, magnetic moment, and bandg…
This manuscript presents a model and simulation of the copper chalcopyrite semiconductor CuGaSe2 in order to predict its magnetic properties. In the semiconductor material CuGaSe2 (CGS), the atom Cu is the only magnetic element with a magnetic moment value S = 1/2. We propose a Hamiltonian to calculate the energies corresponding to different configurations of the system. In a first step, we presented the magnetization behavior by using the Monte Carlo simulations (MCS). The magnetizations as a function of the temperature, the exchange coupling have been studied and discussed. We have also dedu…
A spin model of quasi-one dimensional LiCu$_{2}$O$_{2}$ compound with ground state of ellipsoidal helical structure in which the helical axis is along the diagonal of CuO$_{4}$ squares has been adopted. By taking into account the interchain coupling and exchange anisotropy, the exotic magnetic properties and ferroelectricity induced by spiral spin order have been studied by performing Monte Carlo simulation. The simulation results qualitatively reproduce the main characters of ferroelectric and magnetic behaviors of LiCu$_{2}$O$_{2}$ compound and confirm the low-temperature incollinear spiral …
We present the magnetic properties of complete solid solutions of ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$ cations occupying the A site and magnetic $d^3$ cations on the B site, is a highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations (three unpaired electrons) on the A site as well, exhibits both Néel ferrimagnetism as well as commensurate and incommensurate non-collinear magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for its polar b…
We investigate how the fixed-node diffusion Monte Carlo energy of solids depends on single-particle orbitals used in Slater--Jastrow wave functions. We demonstrate that the dependence can be significant, in particular in the case of 3d transition-metal compounds, which we adopt as examples. We illustrate how exchange-correlation functionals with variable exact-exchange component can be exploited to reduce the fixed-node errors. On the basis of these results we argue that the fixed-node quantum Monte Carlo provides a variational approach for optimization of effective hamiltonians with parameter…
Fluorides in general are characterized by big variety of crystal structures, whereas those containing transition metals also often show sizable magnetic properties. The tendency of fluorine to form linear chain structures in many cases results in low-dimensional magnetism. Despite the plethora of magnetic phenomena in fluorides, their magnetoelectric properties are less studied than those of oxides. In the present work we theoretically study the magnetic and magnetoelectric properties of spin-chain compounds CaFeF$_5$ and SrFeF$_5$. The density functional theory is employed for determination o…
In this paper, we study the critical magnetic properties of the Half Heusler alloy RhCrSi, using Monte Carlo simulations (MCS) under the Metropolis algorithm. In fact, to study this alloy, we apply an Ising model using the MCS simulations, we concentrate only on the magnetic atoms: Rh and Cr. For this purpose, these magnetic atoms are modeled by the spin moments S=5/2 for Rh atoms and sigma=2 for Cr atoms, respectively. In addition, we discuss the ground state phase diagrams in different planes corresponding to different physical parameters. On the other hand, for non-null temperature values, …
New materials are currently sought for use in spintronics applications. Ferromagnetic materials with half metallic properties are valuable in this respect. Here we present the electronic structure and magnetic properties of binary compounds consisting of 3d transition metals and group V elements viz. P, Sb and As in the zinc-blende structure. We demonstrate that compounds of V, Cr and Mn show half metallic behavior for appropriate lattice constants. By comparing the total energies in the ferromagnetic and antiferromagnetic structures, we have ascertained that the ferromagnetic phase is stable …
The fixed node diffusion Monte Carlo (DMC) method has attracted interest in recent years as a way to calculate properties of solid materials with high accuracy. However, the framework for the calculation of properties such as total energies, atomization energies, and excited state energies is not yet fully established. Several outstanding questions remain as to the effect of pseudopotentials, the magnitude of the fixed node error, and the size of supercell finite size effects. Here, we consider in detail the semiconductors ZnSe and ZnO and carry out systematic studies to assess the magnitude o…
The fabrication of ZnSe/ZnTe superlattices grown by the process of rotating the substrate in the presence of an inhomogeneous flux distribution instead of successively closing and opening of source shutters is studied via Monte Carlo simulations. It is found that the concentration of each compound is sinusoidally modulated along the growth direction, caused by the uneven arrival of Se and Te atoms at a given point of the sample, and by the variation of the Te/Se ratio at that point due to the rotation of the substrate. In this way we obtain a ZnSe$_{1-x}$Te$_x$ alloy in which the composition $…
We compute the magnetocaloric effect (MCE) in the GdTX (T=Sc, Ti, Co, Fe; X=Si, Ge) compounds as a function of the temperature and the external magnetic field. To this end we use a density functional theory approach to calculate the exchange-coupling interactions between Gd$^{3+}$ ions on each compound. We consider a simplified magnetic Hamiltonian and analyze the dependence of the exchange couplings on the transition metal T, the p-block element X, and the crystal structure (CeFeSi-type or CeScSi-type). The most significant effects are observed for the replacements Ti $\to$ Sc or Fe $\to$ Co …
Understanding magnetism in multiple magnetic sublattice system, driven by the interplay of varied nature of magnetic exchanges, is on one hand challenging and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6 double double perovskites with multiple magnetic ions both at A- and B-sites, we investigate the mechanism of magnetic behavior in these interesting class of compounds. We find that the magnetism in such multiple sublattice compounds is governed by the interplay and delicate balance between two distinct mechanisms, a) kinetic energy-driven multiple sublattice double…
Using first-principles electronic structure calculations based on the Nth order muffin tin orbital (NMTO)-downfolding technique, we derived the low-energy spin model for CuTe2O5. Our study reveals that this compound is a 2D coupled spin-dimer system with the strongest Cu-Cu interaction mediated by two O-Te-O bridges. We checked the goodness of our model by computing the magnetic susceptibility with the Quantum Monte Carlo technique and by comparing it with available experimental data. We also present magnetization and specific heat results which may be compared with future experimental investi…
Phase diagrams of isoelectronic Eu$_{1-x}$Gd$_x$O and Eu$_{1-x}$Gd$_{x}$S quasi-binary alloy systems are constructed using first-principles calculations combined with the standard cluster expansion approach and Monte-Carlo simulations. The oxide system has a wide miscibility gap on the Gd-rich side but forms ordered compounds on the Eu-rich side, exhibiting a deep asymmetric convex hull in the formation enthalpy diagram. The sulfide system has no stable compounds. The large difference in the formation enthalpies of the oxide and sulfide compounds is due to the contribution of local lattice rel…
We extend our previous first-principles theory for perovskite ferroelectric phase transitions to treat also antiferrodistortive phase transitions. Our approach involves construction of a model Hamiltonian from a Taylor expansion, first-principles calculations to determine expansion parameters, and Monte Carlo simulations to study the resulting system. We apply this approach to three cubic perovskite compounds, SrTiO3, CaTiO3, and NaNbO3, that are known to undergo antiferrodistortive phase transitions. We calculate their transition sequences and transition temperatures at the experimental latti…
Zr and Sc precipitate in aluminum alloys to form the Al\_3Zr\_xSc\_{1-x} compound which, for low supersaturations of the solid solution, exhibits the L1\_2 structure. The aim of the present study is to model at an atomic scale the kinetics of precipitation and to build mesoscopic models so as to extend the range of supersaturations and annealing times that can be simulated up to values of practical interest. In this purpose, we use some ab initio calculations and experimental data to fit an Ising type model describing thermodynamics of the Al-Zr-Sc system. Kinetics of precipitation are studied…
Spin ices are exotic phases of matter characterized by frustrated spins obeying local ice rules, in analogy with the electric dipoles in water ice. In two dimensions, one can similarly define ice rules for in-plane Ising-like spins arranged on a kagome lattice. These ice rules require each triangle plaquette to have a single monopole, and can lead to various unique orders and excitations. Using experimental and theoretical approaches including magnetometry, thermodynamic measurements, neutron scattering and Monte Carlo simulations, we establish HoAgGe as a crystalline (i.e. non-artificial) sys…
The magnetic properties of Li_{1-x}Ni_{1+x}O_2 compounds with x ranging between 0.02 and 0.2 are investigated. Magnetization and ac susceptibility measured at temperatures between 2 K and 300 K reveal a high sensitivity to x, the excess Nickel concentration. We introduce a percolation model describing the formation of Ni clusters and use an Ising model to simulate their magnetic properties. Numerical results, obtained by a Monte-Carlo technique, are compared to the experimental data. We show the existence of a critical concentration, x_c = 0.136, locating the Ni percolation threshold. The syst…
Extensive Monte Carlo simulations are performed to analyze a recent neutron diffraction experiment on a distorted triangular lattice compound RbCoBr$_3$. We consider a spin-lattice model, where both spin and lattice are Ising variables. This model explains well successive magnetic and dielectric transitions observed in the experiment. The exchange interaction parameters and the spin-lattice coupling are estimated. It is found that the spin-lattice coupling is important to explain the slow growth of a ferrimagnetic order. The present simulations were made possible by developing a new Monte Carl…
Path integral Monte Carlo (PIMC) simulations with very simple models were used in order to unveil the physics behind the isotope effects in H-bonded ferroelectrics. First, we studied geometrical effects in the H-bonds caused by deuteration with a general three-site model based on a back-to-back double Morse potential plus a Morse potential between oxygens, fitted to explain different general features for a wide set of H-bonded compounds. Our model results show the Ubbelohde or geometrical effect (GE), i.e., the expansion of the H-bond with deuteration, in agreement to what is observed in H-bon…
Small single crystals of Rb$_3$Ni$_2$(NO$_3$)$_7$ were obtained by crystallization from anhydrous nitric acid solution of rubidium nitrate and nickel nitrate hexahydrate. The basic elements of the crystal structure of this new compound are isolated spin-1 two-leg ladders of Ni$^{2+}$-ions connected by (NO$_3$)$^-$ groups. The experimental data show the absence of long range magnetic order at T $\geq 2$~K. LDA+U calculations and the detailed analysis of the experimental data, i.e. of the magnetic susceptibility, the specific heat in magnetic fields up to 9~T, the magnetization, and of the high-…
Detailed experimental investigations of thermal and magnetic properties are presented for Cu(NH3)4SO4.H2O, an ideal uniform Heisenberg spin half chain compound. A comparison of these properties with relevant spin models is also presented. The temperature dependent magnetic susceptibility and specific heat data has been compared with the exact solution for uniform Heisenberg chain model derived by means of Bethe ansatz technique. Field dependent isothermal magnetization curves are simulated by Quantum Monte Carlo technique and compared with the corresponding experimental ones. Specific heat as …
We investigate the effects of magnetic inhomogeneities and thermal fluctuations on the magnetic properties of a rare earth intermetallic compound, Nd$_2$Fe$_{14}$B. The constrained Monte Carlo method is applied to a Nd$_2$Fe$_{14}$B bulk system to realize the experimentally observed spin reorientation and magnetic anisotropy constants $K^{\rm A}_m (m=1, 2, 4)$ at finite temperatures. % Subsequently, it is found that the temperature dependence of $K^{\rm A}_1$ deviates from the Callen--Callen law, $K^{\rm A}_1(T) \propto M(T)^3$, even above room temperature, $T_{\rm R}\sim 300\rm\, K$, when the…
A comprehensive theoretical and experimental study is presented of the magnetic susceptibility versus temperature χ(T) of spin S = 1/2 two- and three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum Monte Carlo simulations of χ(T) were carried out for both isolated and coupled two-leg ladders with spatially anisotropic intraladder exchange. Accurate fits to these and related literature QMC data were obtained. We have also calculated the one- and two-magnon dispersion relations and the dynamical spin structure factor for anisotropic isolated 2 x 12 ladders. The exchange cons…
An off-lattice, continuous space Kinetic Monte Carlo (KMC) algorithm is discussed and applied in the investigation of strained heteroepitaxial crystal growth. As a starting point, we study a simplifying (1+1)-dimensional situation with inter-atomic interactions given by simple pair-potentials. The model exhibits the appearance of strain-induced misfit dislocations at a characteristic film thickness. In our simulations we observe a power law dependence of this critical thickness on the lattice misfit, which is in agreement with experimental results for semiconductor compounds. We furthermore in…
The insulating iron compounds Eu$_2$SrFe$_2$O$_6$ and Sr$_3$Fe$_2$O$_4$Cl$_2$ have high-temperature antiferromagnetic (AF) order despite their different layered structures. Here we carry out density functional calculations and Monte Carlo simulations to study their electronic structures and magnetic properties aided with analyses of the crystal field, magnetic anisotropy, and superexchange. We find that both compounds are Mott insulators and in the high-spin (HS) Fe$^{2+}$ state ($S$ = 2) accompanied by the weakened crystal field. Although they have different local coordination and crystal fie…
Spin correlations in the geometrically frustrated RBaCo4O7 compounds, usually described as an alternating stacking of Kagome and triangular layers on a hexagonal lattice, have been studied by mean-field approach and by Monte-Carlo simulations. The behavior of the system was modelled with an isotropic Heisenberg Hamiltonian as a function of the relevant parameter Jout/Jin, representing the ratio between exchange integrals inside the Kagome layers, Jin, and between Kagome and triangular layers, Jout. This ratio can be varied in real systems by appropriate chemical substitutions. At the mean-fiel…
Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present more structural complexity with various compositional configurations, such as mixed-alloy, core-shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd-Pt, Cu-Pt, Au-Pt, and Ag-Pt. Within this fra…
Spin crossover molecules have recently emerged as a family of compounds potentially useful for implementing molecular spintronics devices. The calculations of the electronic properties of such molecules is a formidable theoretical challenge as one has to describe the spin ground state of a transition metal as the legand field changes. The problem is dominated by the interplay between strong electron correlation at the transition metal site and charge delocalization over the ligands, and thus it fits into a class of problems where density functional theory may be inadequate. Furthermore, the cr…
Materials with spin-crossover (SCO) properties hold great potentials in information storage and therefore have received a lot of concerns in the recent decades. The hysteresis phenomena accompanying SCO is attributed to the intermolecular cooperativity whose underlying mechanism may have a vibronic origin. In this work, a new vibronic Ising-like model in which the elastic coupling between SCO centers is included by considering harmonic stretching and bending (SAB) interactions is proposed and solved by Monte Carlo simulations. The key parameters in the new model, $k_1$ and $k_2$, corresponding…
The high temperature magnetic order in SrRu$_2$O$_6$ was studied by measuring magnetization and neutron powder diffraction with both polarized and unpolarized neutrons. SrRu$_2$O$_6$ crystallizes into the hexagonal lead antimonate (PbSb$_2$O$_6$, space group \textit{P}$\overline{3}$1\textit{m}) structure with layers of edge-sharing RuO$_6$ octahedra separated by Sr$^{2+}$ ions. SrRu$_2$O$_6$ orders at $T_N$=565\,K with Ru moments coupled antiferromagnetically both in-plane and out-of-plane. The magnetic moment is 1.30(2) $μ_\mathrm{B}$/Ru at room temperature and is along the crystallographic \…
Phaseless auxiliary-field quantum Monte Carlo method with spin-orbit coupling
The Center for Advanced Quantum Studies and School of Physics and Astronomy, Beijing Normal University（北京师范大学量子高级研究中心与物理天文学院）；Key Laboratory of Multiscale Spin Physics (Ministry of Education), Beijing Normal University（北京师范大学多尺度自旋物理教育部重点实验室）；Center for Computational Quantum Physics, Flatiron Institute（Flatiron研究所计算量子物理中心）
Although Boron nitride (BN) is a well-known compound widely used for engineering and scientific purposes, the phase stability of its polymorphs, one of its most fundamental properties, is still under debate. The ab initio determination of the ground state of the BN polymorphs, such as hexagonal and zinc-blende, is difficult because of the elusive Van der Waals interaction, which plays a decisive role in some of the polymorphs, making quantitative prediction highly challenging. Hence, despite multiple theoretical studies, there has been no consensus on the ground state yet, primarily due to con…
Zr and Sc precipitate in aluminum alloys to form the compounds Al3Zr and Al3Sc which for low supersaturations of the solid solution have the L12 structure. The aim of the present study is to model at an atomic scale this kinetics of precipitation and to build a mesoscopic model based on classical nucleation theory so as to extend the field of supersaturations and annealing times that can be simulated. We use some ab-initio calculations and experimental data to fit an Ising model describing thermodynamics of the Al-Zr and Al-Sc systems. Kinetic behavior is described by means of an atom-vacancy …
