Total Energy Calculation and Structure Optimization of Molecule by DV-Xα method

DV-Xα method uses natural and high grade numerical AOs, which generate very precise MOs for a wide variety of molecules within the restriction of LCAO approximation. But Monte-Carlo integration used here causes serious numerical errors for total energy and energy gradient calculation. The author improved their calculation procedure, where the numerical error in physical quantity of a molecule is canceled by the corresponding errors in those of atoms imaginarily isolated from each other. With 2000–4000 sample points per atom, total energy of the molecule including up to period 5 atoms could be calculated precisely. But for energy gradient calculation, far more sample points were necessary and the procedure could be applied only for the molecule including up to period 3 atoms at present. Structure optimization was tried for series of molecules to evaluate its accuracy and performance and then the strategy of further improvement was discussed.