Polarization-Dependent Density Functional Theory: Optical Response
Abstract
The polarization (P) dependence of the exchange-correlation energy (E_xc) results in a new effective field (partial^2E_xc/partialP^2)P≡γP in the Kohn--Sham equations [Gonze et al., PRL 74, 4035], which is absent in LDA. In the long-wavelength limit, γ~=\chi_LDA-1-\chi_exp-1, where \chi is the linear susceptibility. For medium-gap group IV and III--V materials γ is remarkably constant: γ=-0.25±0.02. This value is notably close to the estimate -Δ/(E_g\chi)=-0.23±0.09 re-sulting from a simple quasiparticle analysis, where Eg is the average quasiparticle band gap and Δ the average LDA gap mismatch. However, for materials containing second-row elements (B,C,N,O) γ varies by a factor of two and the simple quasiparticle estimate fails. For the second- and third-order susceptibilities we obtain the Miller-like expressions \chi^(n)_exp~=[\chi_exp/\chi_LDA ]^(n+1)\chi^(n)_LDA, yielding the estimates in the tables. The formula for \chi^ is valid only when \chi^(2)=0. Our \chi^(2) estimate works well for all the materials. Supported by DOE, and the Ohio Supercomputer Center.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1996
- Bibcode:
- 1996APS..MAR.D3135A