Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Polymer Physics V

CPP 28.4: Talk

Thursday, March 29, 2007, 18:00–18:15, H40

Accurate forces in Quantum Monte Carlo calculations with non-local pseudopotentials — •Alexander Badinski and R. J. Needs — Cavendish Laboratory, Cambridge, United Kingdom

Calculating accurate inter-atomic forces within variational and diffusion Monte Carlo (VMC and DMC) methods is a challenging and long-standing problem [1-2]. VMC and DMC methods have become quite successful for calculating ground state total energies of many-electron systems. However the lack of an accurate and efficient method for calculating forces usually requires one to perform VMC and DMC calculations with geometries obtained from either density functional theory or conventional quantum chemistry methods. We present a novel approach to calculate Hellmann-Feynman forces within these two methods using non-local pseudopotentials. The use of pseudopotentials allows one to overcome the severe problem of infinite variance in the sampling distribution of the force estimator which is vital when using statistical methods. Equilibrium geometries and harmonic vibrational frequencies are derived from the forces and compared with those obtained from the energies at the Hartree-Fock, VMC and DMC levels. Results for five small molecules show that the equilibrium bond lengths obtained from the force and energy calculations are in excellent agreement.

[1] R. Assaraf, M. Caffarel, J. Chem. Phys. 119, 10536 (2003) [2] S. Chiesa, D. M. Ceperley, and S. Zhang, Phys. Rev. Lett. 94, 036404 (2005)