New Virial-Theorem-Based Semi-Ab-Initio Method for Atomistic Simulations

摘要

A new semi-ab-initio method for atomistic simulations based on the virial theorem has been suggested. The method is completely within the realm of the density-functional theory and uses the so-called 'reduced' electron spin- density functional (SDF). The crucial component of the method is the ansatz expressing (for both one-component and two-component systems) the electron density at point r as a superposition of 'atomic' densities due to the neighboring atoms. The total energy of this system is shown to consist of three terms. The first depends only on the simulation volume and is independent of the atomic configuration. The second and third, like the embedded-atom method (EAM), are the interatomic pairwise interaction energy, and an 'N-electron' term, which cannot be expressed as an interatomic interaction; it originates from the electron-correlation interaction. The atomic densities are constructed using a set of polynomial-exponential functions resulting in an analytic form for the pair interatomic potential. The coefficients in the atomic density expressions are found using a calibration procedure based on performing a series of ab- initio calculations for a few crystal modifications of this system. Success will depend on whether the charge density in a low-symmetry system under simulation will also be close to the true density obtainable from a meaningful ab-initio calculation; then, the simulation results would be identical to those of the corresponding ab-initio calculation. To what extent the superposition ansatz satisfies this condition is unclear without experimental confirmation.