We present calculations of the magnetic ground states of Cr trimers in different geometries on top of a Au(111) surface. By using a least square fit method based on a fully relativistic embedded-cluster Green's function method first we determined the parameters of a classical vector-spin model consisting of second and fourth order interactions. The newly developed method requires no symmetry constraints, therefore, it is throughout applicable for small nanoparticles of arbitrary geometry. The magnetic ground states were then found by solving the Landau-Lifshitz-Gilbert equations. In all considered cases the configurational energy of the Cr trimers is dominated by large antiferromagnetic nearest neighbor interactions, whilst biquadratic spin-interactions have the second largest contributions to the energy. We find that an equilateral Cr trimer exhibits a frustrated 120$^\circ$ Néel type of ground state with a small out-of-plane component of the magnetization and we show that the Dzyaloshinsky-Moriya interactions determine the chirality of the magnetic ground state. In cases of a linear chain and an isosceles trimer collinear antiferromagnetic ground states are obtained with a magnetization lying parallel to the surface.
Doping-induced spin-manipulation in complex trimer system Ca$_{3}$Cu$_{3}$(PO$_{4}$)$_{4}$: A First Principles Study
用磁性（Ni）和非磁性（Mg）掺杂剂进行自旋操纵掺杂构成了从具有双重基态的线性链海森堡反铁磁Cu基$d^{9}$自旋1/2三聚体化合物Ca $_{3}$ Cu $_{3}$（PO $_{4}$）$_{4}$获得单重态基态系统的实验尝试。本研究是基于第一性原理的调查，这种掺杂的自旋交换机制和电子结构的母体化合物的影响。在获得具有单重态基态的自旋带隙系统方面，用零自旋掺杂剂（如Mg）的位置选择性掺杂被证明比整体自旋掺杂剂Ni更有效，如在实验研究中也观察到的。掺杂诱导的二聚态的基态能量最低。计算出的自旋交换值沿各种可能的路径很好地与早期的实验结果相似。
In this study, we systematically study on crystal and electronic structures and optical absorption properties of perfect monolayer MoS2 (M), M with S vacancy (M@SV), M with N doping at S site (M@ND) and M with both S vacancy and N doping at S site (M@V-D) using first-principles method. It is showed that the N atom is tend to located between Mo and S layers, leaving one vacancy at original site, to form interstitial N atom. Thus, the interstitial N atom and the S vacancy make up the NI-VS dimer. We study M@V-D with five atomic configurations and find the most stable structure having the NI-VS-V…
Incorporating magnetism into two dimensional (2D) van der Waals (VdW) heterostrutures is crucial for the development of functional electronic and magnetic devices. Here we show that Nb3X8 (X = Cl, Br) is a family of 2D layered trimerized kagomé magnets that are paramagnetic at high temperatures and undergo a first order phase transition on cooling to a singlet magnetic state. X-ray diffraction shows that a rearrangement of the VdW stacking accompanies the magnetic transition, with high and low temperature phases consistent with STEM images of the end members α-Nb3Cl8 and \b{eta}-Nb3Br8. The te…
This study examines the magnetic interactions between spatially-variable manganese and chromium trimers substituted into a graphene superlattice. Using density functional theory, we calculate the electronic band structure and magnetic populations for the determination of the electronic and magnetic properties of the system. To explore the super-exchange coupling between the transition-metal atoms, we establish the magnetic magnetic ground states through a comparison of multiple magnetic and spatial configurations. Through an analysis of the electronic and magnetic properties, we conclude that …
The antiferromagnetic kagome material Na2Ti3Cl8 exhibits a first-order phase transition; the low-temperature phase is characterized by the trimerizations of Ti ions. In this work, we carry out first-principles calculations on the crystal and electronic structure of Na$_2$Ti$_3$Cl$_8$ at the high- and low-temperature phases. The crystal structures, including the lattice constant and the trimerization of Ti ions, are well reproduced by taking account a small Hubbard correction of 1 eV. The calculated total energy landscape reveals a first-order phase transition with the total energy barrier of 8…
We study a problem of interacting fractional charges with $J_1$-$J_2$-$J_3$ Ising model on a checkerboard lattice under magnetic field. As a result of the interplay between repulsive interactions and particle density tuning by magnetic field, the fractional charges form a classical spin liquid (CSL) phase. The CSL phase is composed of degenerate spin configurations, which can be mapped to the trimer covering of dual square lattice. The CSL state shows macroscopic ground-state entropy, implying the emergence of novel quantum spin liquid phase when quantum fluctuations are turned on. In addition…
According to the Hohenberg-Kohn theorem of density-functional theory (DFT), all observable quantities of systems of interacting electrons can be expressed as functionals of the ground-state density. This includes, in principle, the spin polarization (magnetization) of open-shell systems; the explicit form of the magnetization as a functional of the total density is, however, unknown. In practice, open-shell systems are always treated with spin-DFT, where the basic variables are the spin densities. Here, the relation between DFT and spin-DFT for open-shell systems is illustrated and the exact m…
Designing electronic magnetoelectric matter with organic quantum spin trimers
Osaka Metropolitan University（大阪公立大学）；University of Florida（佛罗里达大学）；Shanghai Jiao Tong University（上海交通大学）；Osaka Prefecture University（大阪府立大学）；Florida State University（佛罗里达州立大学）；National High Magnetic Field Laboratory, Florida State University（佛罗里达州立大学国家高磁场实验室）
Quantum spin liquid on a 3D bipartite lattice of spin trimers stabilized by enhanced effective anisotropy
Jožef Stefan Institute（约瑟夫·斯特凡研究所）；Faculty of Mathematics and Physics, University of Ljubljana（卢布尔雅那大学数学与物理学院）；Institut Laue-Langevin（朗之万研究所）；Laboratoire Léon Brillouin, CEA, CNRS, Université Paris-Saclay（巴黎萨克雷大学CEA-CNRS莱昂·布里渊实验室）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；Institut Néel, CNRS–UGA（内尔研究所，CNRS-UGA）；Department of Physics, Indian Institute of Technology Tirupati（蒂鲁帕蒂印度理工学院物理系）；Department of Physics and Astronomy and Institute of Applied Physics, Seoul National University（首尔大学天文学与物理学系及应用物理研究所）；Department of Physics, Indian Institute of Technology Madras（马德拉斯印度理工学院物理系）
Spin-1 antiferromagnets are abundant in nature, but few theories or results exist to understand their general properties and behavior, particularly in situations when geometric frustration is present. Here we study the $S=1$ Kagome compound Na$_2$Ti$_3$Cl$_8$ using a combination of Density Functional Theory, Exact Diagonalization, and Density Matrix Renormalization Group methods to achieve a first principles supported explanation of exotic magnetic phases in this compound. We find that the effective magnetic Hamiltonian includes essential non-Heisenberg terms that do not stem from spin-orbit c…
Hexagonal boron nitride (h-BN) is a promising platform for quantum information processing due to its potential to host optically active defects with attractive optical and spin properties. Recent studies suggest that carbon trimers might be the defect responsible for single-photon emission in the visible spectral range in h-BN. In this theoretical study, we combine group theory together with density functional theory (DFT) calculations to predict the properties of the neutral $\text{C}_\text{2}\text{C}_\text{N}$ carbon trimer defect. We find the multi-electron states of this defect along with …
A spin-1 Heisenberg model on trimerized Kagomé lattice is studied by doing a low-energy bosonic theory in terms of plaquette-triplons defined on its triangular unit-cells. The model has an intra-triangle antiferromagnetic exchange interaction, $J$ (set to 1), and two inter-triangle couplings, $J^\prime>0$ (nearest-neighbor) and $J^{\prime\prime}$ (next-nearest-neighbor; of both signs). The triplon analysis of this model studies the stability of the trimerized singlet (TS) ground state in the $J^\prime$-$J^{\prime\prime}$ plane. It gives a quantum phase diagram that has two gapless antiferromag…
A recent study associate carbon with single photon emitters (SPEs) in hexagonal boron nitride (h-BN). This observation, together with the high mobility of carbon in h-BN suggest the existence of SPEs based on carbon clusters. Here, by means of density-functional theory calculations we studied clusters of substitutional carbon atoms up to tetramers in hexagonal boron nitride. Two different conformations of neutral carbon trimers have zero-point line energies and shifts of the phonon sideband compatible with typical photoluminescence spectra. Moreover, some conformations of two small C clusters …
Although many processes of nanostructure evolution in solids occur at elevated temperatures, basic data obtained from ground state energetics are used in the modeling of these phenomena. In order to illustrate the effect of phonon and electron excitations on the free binding energy of defect clusters, first-principles calculations are performed for vacancy-solute pairs as well as vacancy and Cu dimers, trimers, and quadromers in bcc Fe. Based on the equilibrium atomic positions determined by the relaxation of the supercell with the defect in the ground state under constant volume (CV) as well …
Recent experiments have reported that inserting metal atoms or small molecules in between the FeSe layers of $β$-FeSe can significantly enhance the superconducting transition temperature. Here, based on first-principles electronic structure calculations, we propose a stable compound SnOFeSe by alternatively stacking the SnO and $β$-FeSe layers. The predicted SnOFeSe has the same tetragonal structure as the well-known FeAs-based compound LaOFeAs, meanwhile their electronic structures in the nonmagnetic state are quite similar. The magnetic ground state of SnOFeSe is predicted to be the dimer an…
We present a computationally efficient general first-principles based method for spin-lattice simulations for solids. Our method is based on a combination of atomistic spin dynamics and molecular dynamics, expressed through a spin-lattice Hamiltonian where the bilinear magnetic term is expanded to second order in displacement, and all parameters are computed using density functional theory. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and is seen to be in good agreement with previous simulations performed with an empir…
We present a first-principles many-body analysis of multi-orbital lattice susceptibilities in the metallic phase of the quasi-twodimensional compound LiVS$_2$. We base this on advanced correlated electronic structure methods for the $t_{2g}$-shell to reveal a highly entangled spin-orbital hexagonal ordering (SOHO) bringing about an inherently intersite order parameter for the trimerization transition, which eventually leads to an intriguing insulating phase at low temperature.
