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Quantum chemistry by quantum monte carlo: Beyond ground‐state energy calculations
Author(s) -
Reynolds P. J.,
Barnett R. N.,
Hammond B. L.,
Grimes R. M.,
Lester W. A.
Publication year - 1986
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560290403
Subject(s) - quantum monte carlo , diffusion monte carlo , monte carlo method , statistical physics , singlet state , ground state , quantum , physics , schrödinger equation , excited state , monte carlo molecular modeling , quantum mechanics , mathematics , markov chain monte carlo , statistics
We present recent advances with the quantum Monte Carlo (QMC) method in its application to molecular systems. The QMC method is a procedure for solving the Schrödinger equation statistically, by the simulation of an appropriate random process. The formal similarity of the Schrödinger equation with a diffusion equation allows one to calculate quantum mechanical expectation values as Monte Carlo averages over an ensemble of random walks. We have previously obtained highly accurate correlation energies for a number of molecules, as well as the singlet‐triplet splitting in methylene and the barrier height for the H + H 2 exchange reaction. Recently we have begun a program of extending the QMC approach to the calculation of analytic derivatives of the energy. A brief description of the approach is presented here, together with some preliminary results. In addition, we are now computing expectation values of properties other than the energy. We summarize how standard QMC must be modified, and present some results for H 2 and N 2 . Finally, we describe preliminary work toward the goal of obtaining accurate molecular excited states through QMC.