WAVE-FUNCTION-BASED AB INITIO METHODS FOR ELECTRONIC

STRUCTURE CALCULATIONS ON INSULATORS

Alok Shukla

Physics Department, Indian Instititute of Technology, Powai, Mumbai 400076, India (shukla@phy.iitb.ac.in)

Traditionally, the ab initio electronic structure calculations for crystalline systems have been performed within the framework of density functional theory (DFT). However, it is a well-known fact that the DFT does not perform satisfactorily for systems in which electron correlations are strong. As far as excited state properties are concerned, DFT-based approaches systematically underestimate the band-gaps and band-widths of even weakly correlated systems such as semiconductors. Additionally, DFT-based approaches are not amenable to systematic improvements. Therefore, there is a need to go back to the basics and investigate the feasibility of computing the electronic structure of solids via the wave-function route, i.e., by directly solving the Schroedinger equation. The advantages of such an approach are obvious - one can perform both the mean-field (Hartree-Fock) as well as many-body calculations (CI, coupled-cluster etc.) within the same formalism.

Over last several years we have pursued such an approach for crystalline insulators using the Wannier-functions (as against the Bloch orbitals) as the single-particle orbitals, and have performed both Hartree-Fock and the correlated calculations on several ionic and covalent systems. In our talk, we will describe our approach whose implementation resulted in the computer program WANNIER [1,2] and also present results concerning electronic and lattice properties of several crystalline insulators [3,4]. We will argue that such an approach can also be extended to metallic systems, provided one uses a nonorthogonal set of localized orbitals.

References

1 Shukla, A., Dolg, M., Fulde, P. and Stoll, H. (1998) Phys. Rev. B 57, 1471.

2 Shukla, A., Dolg, M., Fulde, P. and Stoll, H. (1999) Phys. Rev. B 60, 5211.

3 Shukla, A. (2000) Phys. Rev. B 61, 13277.

4 Abdurahman, A., Shukla, A. and Dolg, M. (2002) Phys. Rev. B 65, 125204.