Ab initiomulticenter tight-binding model for molecular-dynamics simulations and other applications in covalent systems

A new, approximate method has been developed for computing total energies and forces for a variety of applications including molecular-dynamics simulations of covalent materials. The method is tight-binding-like and is founded on density-functional theory within the pseudopotential scheme. Slightly excited pseudo-atomic-orbitals are used to derive the tight-binding Hamiltonian matrix in real space. The method is used to find the electronic states and total energies for a variety of crystalline phases of Si and the ${\mathrm{Si}}_2$ molecule. Excellent agreement is found with experiment and other first-principles methods. As simple applications of the method, we perform a molecular-dynamics simulated-annealing study of the ${\mathrm{Si}}_3$ molecule to determine the ground-state configuration, and a molecular-dynamics simulation of the spectral density function of the ${\mathrm{Si}}_2$ molecule at high and low excitation levels.