No abstract

A recently proposed tight-binding Hamiltonian model for Selenium ͓Phys. Rev. B 60, 6372 ͑1999͔͒ is modified to incorporate the effect of charge-charge correlations via an empirical Hubbard contribution. The correction term is fitted to reproduce the cohesive energy curve of a finite chain structure while retaining the quality of the tight-binding fit for various rings, infinite chains, and solid phases. The Hubbard corrections are incorporated in the Hellman-Feynman forces via a first-order perturbation theory. The structure and dynamics of various thermodynamics states, obtained from molecular-dynamic simulations in the canonical ensemble, evidence a marked decrease in the number of threefold and onefold defects in the Se chains as a result of the charge-transfer minimization. This translates into a better agreement with ab initio simulation data and experimental evidence, which also reflects in improved estimates for the bond angle distribution functions and the electronic band structure. On the other hand, the pair distribution function and the atomic structure factor are hardly affected by the Hubbard corrections. The minimization of charge transfer brings about the stabilization of longer chains and consequently the microscopic dynamics is also affected, showing both a decrease of the diffusion coefficients and an increase of the bond-stretching band in the vibrational spectrum.

In this work we present an efficient procedure to evaluate effective pair potentials, compatible with "experimental" structure factors, using a Monte Carlo simulation scheme. The procedure does not require the use of inverse Fourier transforms and is robust and rapidly convergent. As a test case the structure factor of liquid Selenium obtained from a Tight-Binding Molecular Dynamics simulation is inverted to obtain an effective pair potential and, as a by-product, the pair distribution function. The inversion procedure yields a pair structure in perfect agreement with the original molecular dynamics calculations and the analysis of the triplet structure and the dynamics also illustrates the limitations of the use of pair potentials in the description of liquids with strongly directional bonding, such as the covalent liquid Selenium.

The structure and dynamics of liquid and supercooled tellurium are investigated using molecular dynamics and an empirical tight-binding Hamiltonian model designed to reproduce ab initio cohesive energies and band structures of various solid phases. Despite the well-known short comings of the reference density-functional theory ab initio calculations, the fitted tight-binding model yields a semiquantitatively correct picture of the dynamics and a relatively good description of the microscopic structure, in fair accordance with the experimental data.