QUMEC: Software for Quantum Mechanics First Principle Calculation in 3-Dimensional Real Space

We present software on total energy calculation by quantum mechanics first principle method with a graphic user interface (GUI). Total energy calculation in this software is based on numerical analysis of time-dependent density functional (the used numerical method is finite difference time domain). QUMEC package has been equipped by common exchange-correlation energy terms with electron spin polarization calculation. With this package, users can calculate the total energy of the free particle, bulk materials, and materials with free surfaces at the atomic scale. The package is tested by several physical subjects, i.e., the surface energy of nano-LiCoO2 and diffusion constant of lithium atoms in LiNi­0.5Mn1.5O4.

Structural, mechanical and thermal properties of Cu2ZnSiS4 with four structures from the first-principle calculations

In this paper, the structural, mechanical and thermal properties of the four structures of Cu2ZnSiS4 were studied on the basis of density functional theory (DFT). The generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) was used to treat the exchange related energy and potential of total energy calculation. The independent elastic constants of the four structures are calculated, which prove that they are mechanically stable. The bulk modulus, Poisson’s ratios and universal anisotropy indices of Cu2ZnSiS4 can be calculated from the obtained elastic constants. In addition, the variation of the bulk modulus with the pressure (0–25 GPa) and temperature (0–700 K) have been reported. In order to further study the compound, the thermal properties of the compound were analyzed by using the quasi-harmonic Debye model, including specific heat, thermal expansion coefficient and Debye temperature.

The nitridoborate nitrides Mg3[BN2]N and Ca3[BN2]N – electronic structure and chemical bonding

The nitridoborates Mg3[BN2]N (P63/mmc) and Ca3[BN2]N (P4/mmm) are electron-precise compounds with discrete linear [BN2]3− and isolated N3− anions. Electronic structure calculations reveal pronounced B–N bonding within the [BN2]3− units with more covalent Mg–N vs. Ca–N bonding. Total energy calculation for hexagonal normal-pressure Mg3[BN2]N, orthorhombic high-pressure Mg3[BN2]N and a hypothetical Ca3[BN2]N-type tetragonal Mg3[BN2]N modification revealed that the hexagonal modification is the ground state structure. The band structure for orthorhombic high-pressure Mg3[BN2]N indicates a substantial metallization (delocalization in the high-pressure regime). This peculiar result calls for a reinvestigation of high-pressure Mg3[BN2]N under different high-pressure high-temperature conditions along with physical property studies.

An ab initio prediction study of the electronic structure and elastic properties of V3GeC2

The electronic structure and elastic properties of the ternary layered carbide V3GeC2 were investigated by the first-principle plane-wave pseudopotential total energy calculation method based on density functional theory. It is found that the computed P63/mmc lattice constants and internal coordinates are a = 2.9636?, c = 17.2256? and zV2 = 0.1325, zC = 0.5712, respectively. The predictable cohesive energy of V3GeC2 reflects that it could be a stable Mn+1AXn phase like Ti3GeC2 and V2GeC, while the band structure shows that the V3GeC2 has anisotropic electrical conductivity, with a high density of states at the Fermi energy. The V3GeC2 exhibits potential anisotropic elastic properties, as well as self-lubricating and ductile behaviour, related to the V-Ge bonds being relatively weaker than the V-C bonds.

Electronic Structure and N-Type Doping in Diamond from First Principles

ABSTRACTAn investigation of the electronic structure of charged vacancies and X(C), X=(As, Sb, P) substitutional centers in diamond has been carried out by means of ab initio density functional theory. The revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) was utilized for the total energy calculation. The equilibrium geometry, defect charge transition levels and energetics of the vacancies and substitutional centers were determined. It is found that substitutional As and Sb introduce a donor level into the band gap about 0.5 eV with respect to the conduction band minimum (CBM), therefore, these elements may be a good choice for achieving n-type diamond. From a technological point of view, however, fabrication of As and Sb doped diamond would be challenging due to its high, positive formation energy.