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J Chem Phys. 2005 Jun 22;122(24):244103.

Electronic quantum Monte Carlo calculations of atomic forces, vibrations, and anharmonicities.

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  • 1The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, 19104-6323, USA.


Atomic forces are calculated for first-row monohydrides and carbon monoxide within electronic quantum Monte Carlo (QMC). Accurate and efficient forces are achieved by using an improved method for moving variational parameters in variational QMC. Newton's method with singular value decomposition (SVD) is combined with steepest-descent (SD) updates along directions rejected by the SVD, after initial SD steps. Dissociation energies in variational and diffusion QMC agree well with the experiment. The atomic forces agree quantitatively with potential-energy surfaces, demonstrating the accuracy of this force procedure. The harmonic vibrational frequencies and anharmonicity constants, derived from the QMC energies and atomic forces, also agree well with the experimental values.

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