Valence and conduction bands of carbon silicon cubic systems are first obtained by a process called linear combination of atomic orbitals Ž . Ž . self-consistent field LCAO-SCF , both at the Hartree-Fock HF and local density Ž . approximation LDA levels. Then, the crystalline orbitals are used in a sum-Ž . over-states SOS method to calculate the corresponding dielectric constants related to electronic polarizabilities. This method allows parallel computations with large granularity of the optical properties and leads to uncoupled HF and LDA results.
Crystalline orbitals obtained by the linear combination of atomic orbitals−self consistent field (LCAO−SCF) method at the Hartree−Fock (HF) and Kohn−Sham (KS) levels, are used to calculate the polarizability
and related functions such as dielectric constant, reflectance, and energy-loss function (ELF). Comparison of
our calculations with experiment leads to a satisfactory agreement. The ELF spectra show clearly the energy
ranges corresponding to the electronic excitations of the different orbitals. The carbon K-edge range is accurately
analyzed in connection with the density of states.
Compton profiles, polarizabilities and related functions of diamond and cubic boron nitride have been investigated within the Hartree-Fock approximation and the density functional theory, calculated within the local density approximation and generalized gradient approximation, but without any explicit correlation correction for the Compton profiles. The correlation part already included in the standard uncorrected density functional theory is deduced from the comparison of the two types of calculation. The Compton profile and reciprocal-form-factor anisotropies, polarizability, dielectric constant and energy loss function of the two compounds are compared at the same level of accuracy. These properties are very close in spite of the rather different chemical bonds due to the charge transfer occurring in cubic boron nitride and gaps.
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