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Pseudopotential Hartree-fock Study of 17 Iii-v-semiconductors and Iv-iv-semiconductors
No full textThe binding energy (BE), the equilibrium lattice parameter (alpha-0), the bulk modulus (B), and the central-zone transverse-optical phonon frequency (v) of seventeen diamond- and zinc-blende-type-structure semiconductors involving atoms belonging to the second to fifth periods have been evaluated. The periodic ab initio Hartree-Fock linear-combination-of-atomic-orbitals program CRYSTAL has been used. Core pseudopotentials have been adopted in order to limit the calculation to valence electrons. Thirteen atomic orbitals (2s, 6p, 5d) per atom have been used. The quality of the pseudo-potential results is checked by comparison with all-electron calculations performed on six light-atom systems (diamond, silicon, BN, BP, AlP, SiC). The mean errors of the pseudopotential calculations with respect to experimental data are -38%, +1.2%, +6.5%, and +7.8% for BE, alpha-0, B, and v, respectively. A correlation-only density-functional alpha-posteriori correction to the Hartree-Fock total energy is performed, which reduces the absolute BE mean error to 2.6%
Periodic Hartree-fock Study of A Weakly Bonded Layer Structure - Brucite Mg(oh)2
No full textThe layered mineral brucite Mg(OH), is investigated theoretically using an ab initio all-electron linear combination of atomic orbitals Hartree-Fock (HF) approximation. At the HF level, the interlayer interaction is weak and the interlayer distance is larger than the experimental one. Bonding is discussed on the basis of density of states and charge-density maps. No hydrogen bond is characterized. A posteriori correction of the energy for the correlation error is performed by use of the functional approach. The three semilocal functional formulas used yield similar results. This brings in extra interlayer bonding interaction, and yields a calculated geometry in agreement with experiments. The analysis of the interlayer bondings shows that it is mainly of dispersion type, and that the used functionals account for dispersion, in particular at short interatomic distances
Non-empirical Pseudopotentials In the Hf-lcao Approach To Crystalline Solids - Comparison To All-electron Results
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Quantum-mechanical Hartree-Fock study of calcite at variable pressure, and comparison with magnesite
No full textThe static crystal energy of calcite and its structure configuration as functions of pressure were determined by ab initio all-electron periodic Hartree-Fock calculations (CRYSTAL code). Ca, O and C atoms were represented by 22, 18 and 14 atomic orbitals, respectively, in form of contracted Gaussian-type functions. Comparison between theoretical and experimental data was performed for binding energy, equilibrium unit-cell and bond lengths, bulk modulus and C33 and C11 + C12 elastic constants, and vibrational frequency of the symmetrical C-O stretching mode. The agreement is generally satisfactory. A larger compressibility is observed for structural parameters of calcite than for those of magnesite coming from a similar calculation. The Ca-O and C-O chemical bonding was characterized by electron density maps and by Mulliken atomic charges; these are discussed and compared to values determined by empirical fitting of Born-type interatomic potentials
Hartree-fock Abinitio Characterization of Ionic-crystal Surfaces With A Slab Model - the (0001) Face of Alpha-al2o3
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