氢吸附金刚石（001）表面的第一性原理研究

采用第一性原理方法研究氢吸附的金刚石（001）表面，计算了氢吸附金刚石表面构型.通过分析吸附前后空间电荷分布的变化，发现吸附H原子的金刚石（001）表面电荷向H原子转移，即表明氢吸附的金刚石表面带负电.分析了这种现象的微观机制，以及它对金刚石表面电学性质的影响. 关键词： 第一性原理计算 金刚石（001）面 表面吸附 电荷密度分布     

氘、氚代聚苯乙烯单体abinitio研究

用HF,MP2及BLYP从头算方法,在6—31G基组水平上,优化了聚苯乙烯单体基态的平衡几何构型.主要用BLYP6—31方法研究了氘、氚代聚苯乙烯单体(DPS,PST)的正则振动频率、红外光谱强度、C—D键键能,并对正则振动模式进行了简单分析,同时研究了DPS,PST单体中温度、压强与熵的关系. 关键词： 平衡几何构型 正则振动频率 红外光谱强度 键能     

Ab initio study of ion-pair states of I2 molecule

This paper reports on ab initio study of the ion-pair states of the I₂ molecule, correlating to I⁺(³ P _{J=2, 1, 0}, ¹ D ₂) + I^?(¹ S ₀) dissociation asymptotes. Calculations are in a rather good agreement with experiment and explain key features of the ion-pair states structure including in particular the remarkable similarity of the gerade state potentials in comparison with the ungerade ones which significantly differ in shape and equilibrium internuclear distance. The dipole moment functions were calculated for the transitions between ion-pair states, correlating to a common and different dissociation thresholds. The dipole moment functions for this type of transitions have been obtained for the first time and are or special interest in the context of resent experimental studies of the amplified spontaneous emission effect on transitions between ion-pair states.     

Ab initio study on magnetism at GaN (100) and (101) surfaces

The magnetism of GaN (100) and (101) surfaces containing neutral intrinsic defects has been investigated using ab inito calculations. Ideal Ga-ended GaN (100) surfaces and (101) surfaces are nonmagnetic. After surface relaxation, an N-ended GaN (100) surface transforms to a Ga-end, which presents local magnetic moments being ferromagnetically coupled. Neutral gallium vacancies at the (100) surface bring about large magnetic moments, which are ferromagnetically coupled. The spin-polarization of 2p electrons of nitrogen atoms is responsible for the induced magnetic moments. Neutral nitrogen vacancies at the (101) surface induce a zero magnetic moment. Neutral gallium vacancies at the (101) surface might lead to an antiferromagnetic state.     

A new quaternary semiconductor compound (Ba2Sb4GeS10): Ab initio study

Abstract

The newly synthesised Ba₂Sb₄GeS₁₀ compound is notable because of the interesting features of the quaternary Sb-containing materials. The first principle method has been used to determine the physical properties of this compound. In particular, the electronic structure has been analysed using both conventional GGA-PBE and HSE06 functional. The values of the band gap for PBE and HSE06 calculations were 1.324 and 1.84 eV, respectively. The calculated elastic constants were used to predict polycrystalline mechanical properties. The estimated Vickers hardness (2.7 GPa) values show that Ba₂Sb₄GeS₁₀ is soft matter. Moreover, the vibrational properties of the compound have been studied. The calculation of the elastic constants and phonon dispersion curves indicates that the Ba₂Sb₄GeS₁₀ compound is stable both mechanically and dynamically. Furthermore, the minimum thermal conductivity and optical properties, such as dielectric functions and energy loss function, have also been discussed in detail in this paper.     

Ab initio study of graphene on SiC

Employing density-functional calculations we study single and double graphene layers on Si- and C-terminated 1x1-6H-SiC surfaces. We show that, in contrast with earlier assumptions, the first carbon layer is covalently bonded to the substrate and cannot be responsible for the graphene-type electronic spectrum observed experimentally. The characteristic spectrum of freestanding graphene appears with the second carbon layer, which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, the interface is metallic, whereas on C face it is semiconducting or semimetallic for single or double graphene coverage, respectively.     

Ab initio study of PrAg intermetallic compound

In this work, a first-principles study on PrAg compound using the density functional theory implemented in the projector-augmented wave (PAW) method in the CsCl (B2) crystal structure has been performed. Based on the optimized structural parameter, which is in good agreement with experimental data, the electronic structure, elastic, thermodynamics and vibrational properties have been investigated. The temperature and pressure variations of volume, bulk modulus, thermal expansion coefficient, heat capacities, and Debye temperatures in wide pressure (0-30 GPa) and temperature ranges have also been predicted.     

Ab initio study of the electronic structure of the molecule-based ferromagnet Co[N(CN)2]2

We have investigated the electronic and magnetic properties of the molecule-based magnet Co[N(CN)₂]₂ using the full potential linearized augmented plane wave (FP-LAPW) method. The relative stability of the ground state, density of states and charge distributions were examined. Total energy calculations reveals that the ferromagnetic phase is a stable ground state for Co[N(CN)₂]₂ in agreement with the previous experimental findings. It is noteworthy that we predict the Co[N(CN)₂]₂ is a ferromagnetic semiconductor with a small band gap of 0.027 eV, and the semiconductor property can be connected to the strong crystal field splitting of Co²⁺ 3d states for Co[N(CN)₂]₂. Such a molecule-based ferromagnetic semiconductor would offer a potential for semiconductor applications, therefore, an experimental confirmation of our theoretical predictions is encouraged.     

Ab initio study of SrTiO3 surfaces

We present first-principles total-energy calculations of (001) surfaces of SrTiO₃. Both SrO-terminated and TiO₂-terminated surfaces are considered, and the results are compared with previous calculations for BaTiO₃ surfaces. The major differences are in the details of the relaxed surface structures. Our calculations argue against the existence of a large ferroelectric relaxation in the surface layer, as had been previously proposed. We do find some indications of a weak surface ferroelectric instability, but so weak as to be easily destroyed by thermal fluctuations, except perhaps at quite low temperatures. We also compute surface relaxation energies and surface electronic band structures, obtaining results that are generally similar to those for BaTiO₃.     

Ab initio MRD-CI investigation of the electronic spectrum of glyoxal (CHO)2

Multireference configuration interaction (MRD-CI) calculations are used to compute the electronic spectrum of glyoxal (CHO)₂, a key species in atmospheric chemistry. The calculations place the first dipole-allowed transition 1¹A_u←X¹A_g at 2.80?eV (442.8?nm) with an oscillator strength of 0.0002 and the dipole forbidden 1¹B_g?←?X¹A_g transition at 4.22?eV (293.8?nm), in accordance with prior experiments. In addition, a much stronger transition (3¹B_u?←?X¹A_g) at 8.51?eV (145.7?nm) is predicted, which has not yet been reported in the literature. This transition corresponds to 1b_g?→?2a_u excitation and can be characterized as π(CO)?→?π?(CO) type in accordance with the computed relatively large oscillator strength f?=?0.38. The corresponding triplet states are also computed.     

Ab initio study of platinum induced reconstructions on Ge(001)-(1×2) surface with dimerization

We present first principle total energy calculation of Pt induced reconstructions on Ge(001)-(1×2) surface with dimerization. Study was undertaken using localized orbitals basis set DFT using SIESTA to compare pure Ge dimerized Ge(001)-(1×2) surface with 0.5 and 1.0 Pt covered dimerized Ge(001)-(1×2) surface with the possibility of homo (Ge-Ge and Pt-Pt) and hetro (Pt-Ge) dimers. From total energy calculation results we calculated dimer bond lengths, buckling angles and formation energy of dimers on Ge(001)-(1×2) surface. By calculating the formation energy of different configurations we find that Ge-Ge buckled dimerized surface has least (−1.23 eV/dimer) and Pt-Pt symmetric dimerized surface has largest (+0.09 eV/dimer) formation energy with respect to unreconstructed surface. We further calculated the electronic DOS and band structure of Ge dimerized as well as Pt dimerized surface to see the change in semiconducting behavior on dimerization. By comparing the DOS and electronic band structure of homo Ge dimerized surface, we found metallicity of Ge(001)-(1×2) surface results from dimer formation. Also by comparing the electronic band structure of homo Ge dimerized surface with unreconstructed surface we find that less number of bands crossing the Fermi level which is perhaps due to the saturation of one dangling bond per Ge surface atom. By introducing Pt at 0.5 and 1.0 coverage in place of Ge, except for homo Pt buckled dimerized surface having 1.0 coverage of Pt, we find in all other cases increase in number of bands are crossing the Fermi level, indicating strong metallic behavior of Ge(001)-(1×2) surface.     

Ab initio investigation of the CdTe (001) surface

Based on first-principles density functional pseudopotential calculations, the CdTe (001) surface has been studied. Atomic configurations of different reconstructions are obtained with good accuracy. This reveals the efficiency of the force calculation for the surface relaxations. The surface energies were calculated on relaxed surface slabs as a function of the chemical potentials. The main result is that the energy of the Te-terminated dimerized surface with a (2 × 1) reconstruction is larger than the Cd-terminated c(2×2) reconstructed surface. This is in agreement with what was suspected by the equilibrium model introduced by F. Tinjod et al., which explains the formation of the quantum dots in CdTe/ZnTe superstructures.     

(CuIn)_n(n=1,2)小团簇的结构与稳定性的从头算理论研究

本文采用从头算理论MP2方法研究了合金团簇(Cu In)n(n=1,2)的结构和稳定性.计算得到的双原子分子Cu In几何参数、频率和解离能跟实验数据十分吻合.(Cu In)2团簇有五个稳定结构,基态结构是具有1A1/C2v对称性的蝴蝶结构,结合能为6.57 e V.将计算结果与同族元素体系(Cu Al)2和(Cu Tl)2对比,无论是在构型上,还是在电子特性上都有相似性.文中给出了(Cu In)2稳定构型的电子结合能能谱,希望在实验上得以验证.     

Ab initio study of magnetic property of BEST2 [Fe(CN)5NO] charge-transfer salt

By means of ab initio method of the full potential linearized augmented-plane-wave, electronic band structure and its magnetic property for a charge transfer compound of bis (ethylenediselena)-tetrathiafulvalene(BEST) with [Fe(CN)₅NO] anions are investigated for the first time, where the exchange-correlation effects of electrons are accounted in the generalized gradient approximation. The spin density of states and the magnetic moment are analyzed in detail. It is found that there exists a new antiferromagnetic coupling in the organic donors because of alternating spin population in the organic donors. Besides the localized 3d electrons of Fe in [Fe(CN)₅NO] anion, the ligand nitric oxide and the cyanogen radical play important roles in the magnetic properties of the system. Our results are in good agreement with the experimental observations.     

Ab initio study of electronic structure and magnetic properties of copper (II) terephthalate

The first principles within the full potential linearized augmented plane wave (FP-LAPW) method was applied to study the compound of Cutp(OH₂)₂. The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has a ferromagnetic interaction arising from the bridging water molecule. The spin magnetic moment 1.0μ_B per molecule mainly comes from the Cu ion with little contribution from O, C anion.