We present a study of the thermodynamic and physical properties of Ta5Si3 compounds by means of density functional theory based calculations. Among the three different structures (D8m, D8l, D88), the D8l structure (Cr5B3-prototype) is the low temperature phase with a high formation enthalpy of -449.20kJ/mol, the D8m structure (W5Si3-prototype) is the high temperature phase with a formation enthalpy of -419.36kJ/mol, and the D88 structure (Mn5Si3-prototype) is a metastable phase. The optimized lattice constants of the different Ta5Si3 compounds are also in good agreement with the experimental data. The electronic density of states (DOS) and the bonding charge density have also been calculated to elucidate the bonding mechanism in these compounds and the results indicate that bonding is mostly of covalent nature. The elastic constants of the D8m and D8l structures have been calculated together with the different moduli. Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion and the Grüneisen parameter have also been obtained in the present work. The transformation temperature (2303.7K) between the D8m and the D8l structures has been predicted by means of the Gibbs energy, and this predicted temperature (2303.7K) is close to the experimental value (2433.5K).
Although many binary compounds have the B2 (CsCl-type) structure in the thermodynamic phase diagram, an origin of the structural stability is not understood well. Here, we focus on 416 compounds in the B2 structure extracted from the Materials Project, and study the dynamical stability of those compounds from first principles. We demonstrate that the B2 phase stability lies in whether the lowest frequency phonon at the $M$ point in the Brillouin zone is endowed with a positive frequency. We show that the interatomic interactions up to the fourth nearest neighbor atoms are necessary for stabili…
We investigate the charge density distribution in titanium dioxide, molecular titanium complexes and a variety of periodic titanium compounds using delocalization indices and Bader charge analysis. Our results are in agreement with previous experimental and theoretical investigations on the charge stability and deviation from formal oxidation states in transition metal compounds. We present examples for practically relevant redox processes, using molecular titanium dioxide model systems, that illustrate the failure of formal oxidation states to account for some redox phenomena. We observe a pr…
Prediction of topological insulating behavior in Hg2CuTi-type Heusler compounds from first principles
采用密度泛函理论中的第一性原理计算，研究了具有Hg 2CuTi结构的X2 YZ Heusler化合物的拓扑能带结构.我们的研究结果清楚地表明，大量的Hg_2CuTi型Heusler化合物自然地表现出明显的带反转特征，这主要是由Y-Z锌双晶亚晶格控制的。Hg 2CuTi型Heusler化合物与半Heusler族化合物相似，其拓扑能带阶对晶格常数的变化非常敏感，且大多数化合物具有负的形成能，这使得它们更适合于材料生长，并且通过合金化或适当的应变可以容易地实现拓扑绝缘行为。
The performance of density functional theory (DFT) approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental phases, ΔHf. However, a compound competes thermodynamically with both other compounds and their constituent elemental forms, and thus, the enthalpies of the decomposition reactions to these competing phases, ΔHd, determines thermodynamic stability. We evaluated the phase diagrams for 56,791 compounds to classify decomposition reactions into three types: 1. those that produce e…
First-principles calculations were performed, and the results from the study of structural, electronic and elastic properties of zincblende III-arsenide binary compounds (BAs, AlAs, GaAs and InAs) are presented. These properties have been calculated using an ab initio pseudopotential method based on density functional theory (DFT) with the local density approximation (LDA) for the exchange-correlation potential. The results obtained for the calculated properties have been compared with experimental data and other computational works. It has also been found that our results with LDA are in good…
We investigate the effects of various dopants (M = K--Br) on the Curie temperature of the magnetic compound NdFe12 through first-principles calculations. Analysis by the Korringa--Kohn--Rostoker method with the coherent potential approximation reveals that doping the Fe sites with optimal concentrations of Ge and As is a promising strategy for increasing the Curie temperature. To search over a wider space, we also perform Bayesian optimization. Out of over 180,000 candidate compositions, co-doped systems with Co, Ge, and As are found to have the highest Curie temperatures.
Lattice defects affect the long-term stability of halide perovskite solar cells. Whereas simple point defects, i.e., atomic interstitials and vacancies, have been studied in great detail, here we focus on compound defects that are more likely to form under crystal growth conditions, such as compound vacancies or interstitials, and antisites. We identify the most prominent defects in the archetype inorganic perovskite CsPbI$_3$, through first-principles density functional theory (DFT) calculations. We find that under equilibrium conditions at room temperature, the antisite of Pb substituting Cs…
Physical properties of Thallium-Tellurium based thermoelectric compounds using first-principles simulations
采用密度泛函理论计算方法，研究了Tl_5Te_3，BiTl_9Te_6和SbTl_9Te_6化合物的热力学和物理性质.优化得到的化合物晶格常数与实验值符合较好。计算了三种化合物的电子态密度和能带结构，以了解它们的成键机制。BiTl 9 Te 6和SbTl 9 Te 6化合物的间接带隙分别为0.256eV和0.374eV。自旋-轨道耦合对两种半导体化合物的电子结构有重要影响，因此应该包括这些材料的良好的数值描述。计算了这三种化合物的弹性常数，测定了它们的体积模量、剪切模量和杨氏模量。Sb、Bi合金化后的韧脆转变与电子性质的变化有关。最后，得到了德拜温度、纵向声速、横向声速和平均声速。
Study of the structural and electronic properties of semimetallic InBi: first-principles calculation of compound with peculiarities of the electronic structure
First-principles prediction of redox potentials in transition-metal compounds with LDA+U
局域密度近似（LDA）或广义梯度近似（GGA）中的第一性原理计算虽然非常成功，但已知低估了氧化还原电位，例如锂嵌入过渡金属化合物的氧化还原电位。我们认为，这种不准确性与LDA/GGA中电子自相互作用误差的抵消不足有关，并且可以通过使用DFT+ $U$方法对$U$参数进行自洽评估来改善。我们表明，使用这种方法，实验嵌锂电压的过渡金属化合物，包括橄榄石锂$_{x}$ MPO $_{4}$（M=Mn，Fe Co，Ni），层状锂$_{x}$ MO $_{2}$（$x=$ Co，Ni）和尖晶石样锂$_{x}$ M $_{2}$ O $_{4}$（M=Mn，Co），可以准确地再现。
AB5 compounds (A = rare earth, B = transition metal) have been widely studied as anodes for Ni-MH applications. However, they have reached their technical limitations and the search for new promising materials with high capacity is foreseen. ABy compounds (2 < y < 5) are good candidates. They are made by stacking [AB5] and [A2B4] units along the c crystallographic axis. The latter unit allows a large increase in capacity, while the [AB5] unit provides good cycling stability. Consequently, the AB3.8 composition (i.e. A5B19 with three [AB5] for one [A2B4]) is expected to exhibit better cycling s…
Direct energy bandgap materials are crucial for the efficient optoelectronics devices. Therefore, the investigation of new direct gap materials is important. In the present work, two novel d-metal sulfides Sc2CdS4 and Y2CdS4 compounds are investigated by using the all electron full potential linearized augment plane wave method. Both the compounds show semiconducting nature and direct band gap with a value 1.886eV for Sc2CdS4 and 2.209eV for Y2CdS4, respectively. Strong hybridization between S-p and Sc/Y-d orbitals present among valence and conduction bands which is beneicial to electrical tra…
We have performed systematic density functional calculations and evaluated thermoelectric properties, See- beck coefficient and anomalous Nernst coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The carrier concentration dependence of Seebeck coefficients in nonmagnetic compounds are in good agreement with experimental values. We found that the half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect originating from Berry curvature at the Brillouin zone boundary. These results help to understanding for the mechanism of large anomalous Nernst coefficient and giv…
Using first principles calculations, the energetic stability of two-dimensional (2D) binary compounds $XY$ is investigated, where $X$ and $Y$ indicate the metallic element from Li to Pb in the periodic table. Here, 1081 compounds in the buckled honeycomb (BHC), buckled square, B2, L1$_0$, and B$_h$ structures are studied. For the compounds that have negative formation energy in the BHC structure or the compounds that can have the B$_h$ structure, the phonon dispersions of the 2D structures are also calculated. We demonstrate that (i) a negative formation energy is neither a sufficient nor nece…
Recent attempts at topological materials have revealed a large class of materials that show gapless surface states protected by time-reversal symmetry and crystal symmetries. Among them, topological insulating states protected by crystal symmetries, rather than time-reversal symmetry are classified as topological crystalline insulators. We computationally predict the signature of new three-dimensional topological crystalline insulating compounds of space group 139(I/4mmm). After conducting a full volume optimization process by allowing to rearrange of atomic positions and lattice parameters, t…
Honeycomb structure has been frequently observed in two-dimensional (2D) materials. CuAu in the buckled honeycomb (BHC) structure has been synthesized recently, which is the first case of 2D intermetallic compounds. Here, the dynamical stability of 2D $AX$ in the BHC structure, where $A=$ Cu, Ag, and Au and $X$ is a metallic element in the periodic table, is systematically studied by calculating phonon dispersions from first-principles. Among 135 $AX$, more than 50 $AX$ are identified to be dynamically stable. In addition, (i) a relationship between the dynamical stability and the formation en…
Topological nontrivial nature are the latest phases to be discovered in condensed matter physics with insulating bulk band gaps and topologically protected metallic surface states; they are one of the current hot topics because of their unique properties and potential applications. In this paper, we have highlighted a first-principles study of the structural stability and electronic behavior of the Na${}_{2}$AgX (X= As, Sb and Bi) full Heusler compounds, using the Full-Potential Linear Muffin-Tin Orbital (FP-LMTO) method. We have originated that the Hg${}_{2}$CuTi structure is appropriate in a…
Pressure-induced insulator-to-metal transition (IMT) has been studied in the van der Waals compound iron thiophosphate (FePS3) using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid Hartree-Fock-DFT B3LYP functional. Our calculations reproduce correctly the IMT at ~15 GPa, which is accompanied by a reduction of the unit cell volume and of the vdW gap. We found from the detailed analysis of the projected density of states that the 3p states of phosphorus atoms contribute significantly at the bottom of the conduction band. As a result, th…
Magnetovolume Effects in Heusler Compounds via First-Principles Calculations
Heusler合金由于具有高的磁热效应和磁体积效应，在包括磁制冷在内的多种应用中具有广阔的前景。优化这种潜力的一种方法是通过增加磁体积效应。采用密度泛函理论和Korringa-Kohn-Rostoker方法，计算了几种L2 1型Co2 YZ Heusler合金的有效交换相互作用能和相应的平均场居里温度随体积（静水压力）的变化.不同的定性趋势和迹象的居里温度和力矩的压力导数中发现这些化合物，讨论和以前的计算和实验进行比较。
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…
The spin-orbit -induced spin splitting of energy bands in low symmetry compounds (the Rashba Effect) has a long-standing relevance to spintronic applications and to the fundamental understanding of symmetry breaking in solids, yet the knowledge of what controls its magnitude in different materials is difficult to anticipate. Indeed, rare discoveries of compounds with large Rashba coefficients are invariably greeted as pleasant surprises. We advance the understanding of the "Rashba Scale" using the "inverse design" approach by formulating theoretically the relevant design principle and then ide…
Structural stability, electronic band structure, and optoelectronic properties of quaternary chalcogenide CuZn2MS4 (M =In and Ga) compounds via first principles
The structural stability of CeFe$_{12}$ is investigated by using first-principles calculation. The formation energies of CeFe$_{12}$ relative to the Ce$_{2}$Fe$_{17}$ + bcc-Fe phase and to the CeFe$_{2}$ + bcc-Fe phase are calculated with the assumptions of trivalency and tetravalency for Ce. Those values are compared with corresponding results in $R$Fe$_{12}$ for $R=$ Nd, Sm, and Zr. Our results suggest that the tetravalent Ce is a promising stabilizer of the ThMn$_{12}$ structure. We also show that the stabilizing effect of an element depends as much on the valency as on the size of the $R$ …
First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In)
In this work the electronic properties of Fe doped CuO thin films are studied by using a standard density functional theory. This approach is based on the abinitio calculations under the Korringa Kohn Rostoker coherent potential approximation. We carried out our investigations in the framework of the general gradient approximation and self interaction corrected. The density of states in the energy diagrams are presented and discussed. The computed electronic properties of the studied compound confirm the half metalicity nature of this material. In addition, the absorption spectra of the studie…
Ni-Mn based ternary Heusler compounds have drawn attentions lately as significant magneto-caloric effects in some of them have been observed. Substitution of Ni and Mn by other $3d$ transition metals in controlled quantity have turned out to be successful in enhancing the effect and bring the operational temperatures closer to the room temperature. Using density functional theory calculations, in this work, we have systematically explored the roles of various factors such as site occupancies, magnetic interactions, and compositions associated with the constituents of Mn-excess Ni$_{2}$MnSb Heu…
It is generally assumed in the thermoelectric community that the lattice thermal conductivity of a given material is independent of the electronic properties. This perspective is however questionable since the electron-phonon coupling could have certain effects on both the carrier and phonon transport, which in turn will affect the thermoelectric properties. Using SiGe compound as a prototypical example, we give an accurate prediction of the carrier relaxation time by considering scattering from all the phonon modes, as opposed to the simple deformation potential theory. It is found that the c…
We investigate the structural, electronic, mechanical and elastic properties of two niobium based intermetallic compounds Nb3Be and Nb3Be2 by using the DFT based theoretical method. A good agreement is found among the structural parameters of both the phases with experimentally evaluated parameters. For both the phases metallic conductivity is observed while Nb3Be phase is more conducting than that of Nb3Be2 phase. Evaluated DOS at Fermi level indicates that Nb3Be2 phase is electrically more stable than Nb3Be phase. For both phases Nb-4d states is mostly responsible for metallic conductivity. …
The structural, electronic and magnetic properties of half-Heusler compounds XVSb (X $=$ Fe, Co and Ni) are investigated by using the density functional theory with generalized gradient approximation (GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential approximation. It is found that the half-metallic gaps are generally reasonably widened by mBJ as compared to the GGA approximation. The magnetic proprieties of XVSb (X $=$ Fe, Co and Ni) are well defined within mBJ with an exact integer value of magnetic moment. The band gaps given by TB-mBJ are in good agreement with the av…
