Optimization of a distributed Gaussian basis set using simulated annealing: Application to the solvated electron

Abstract

A distributed Gaussian basis set is employed to calculate the energy eigenvalues and eigenstates of an electron solvated in a molecular fluid. A combination of two techniques is proposed to optimize the basis functions. The first consists of treating the centers of the Gaussians as dynamical variables whose optimal distribution for a given solvent configuration is obtained by the technique of simulated annealing. In addition, the Gaussian basis functions are multiplied by Jastrow factors which suppress excessive overlap within the repulsive cores of the solvent molecules. The method is applied to a series of rigid solvent configurations sampled from a path integral Monte Carlo simulation of an electron solvated in ammonia. A careful comparison is made with averages derived from the path integral calculations. The two methods are found to agree within 10% for the ground state energy. From the sample of different solvent configurations the adiabatic fluctuation in the energy eigenvalues and the density of states is analyzed and compared to experimental data.