Total energy and pressure in the Gaussian-orbitals technique. I. Methodology with application to the high-pressure equation of state of neon

Abstract

Callaway, Zou, and Bagayoko [Phys. Rev. B 27, 631 (1983)] (CZB) have presented algorithms for extracting crystalline total energies from Fourier-transform, linear combinations of Gaussian-type orbitals (LCGTO's), local-density-functional electronic-structure calculations. To obtain stable total energies as well as direct (i.e., virial theorem) pressures for a wide variety of systems, the CZB algorithms must be modified to remove unphysical numerical instabilities, achieve crucial cancellations, etc. Excellent results are obtained for bcc Li with these techniques and an appropriately enriched basis. Equation-of-state studies on a prototype molecular crystal, fcc Ne, reveal difficulties related to the Fourier-transform techniques. The most important is the approximate treatment (the linear term in a density shift expansion) of the iterative improvement of the exchange-correlation-potential Fourier coefficients. These difficulties are completely controlled and the density expansion is rendered rapidly convergent by use of an improved version of the augmented-plane-wave to LCGTO conversion technique previously reported. That procedure is used to predict the fcc Ne equation of state to 2.8 Mbar as an extension of the 0-150-kbar experimental data. The calculated high-pressure electronic structure also yields a secondary prediction: There is no metallization in the fcc phase through 2.8 Mbar.