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Title: Quantum Monte Carlo for vibrating molecules

Abstract

Quantum Monte Carlo (QMC) has successfully computed the total electronic energies of atoms and molecules. The main goal of this work is to use correlation function quantum Monte Carlo (CFQMC) to compute the vibrational state energies of molecules given a potential energy surface (PES). In CFQMC, an ensemble of random walkers simulate the diffusion and branching processes of the imaginary-time time dependent Schroedinger equation in order to evaluate the matrix elements. The program QMCVIB was written to perform multi-state VMC and CFQMC calculations and employed for several calculations of the H{sub 2}O and C{sub 3} vibrational states, using 7 PES`s, 3 trial wavefunction forms, two methods of non-linear basis function parameter optimization, and on both serial and parallel computers. In order to construct accurate trial wavefunctions different wavefunctions forms were required for H{sub 2}O and C{sub 3}. In order to construct accurate trial wavefunctions for C{sub 3}, the non-linear parameters were optimized with respect to the sum of the energies of several low-lying vibrational states. In order to stabilize the statistical error estimates for C{sub 3} the Monte Carlo data was collected into blocks. Accurate vibrational state energies were computed using both serial and parallel QMCVIB programs. Comparison of vibrationalmore » state energies computed from the three C{sub 3} PES`s suggested that a non-linear equilibrium geometry PES is the most accurate and that discrete potential representations may be used to conveniently determine vibrational state energies.« less

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States). Chemistry Dept.
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Energy Research, Washington, DC (United States)
OSTI Identifier:
414375
Report Number(s):
LBNL-39574
ON: DE97001595; TRN: 97:001798
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: DN: Thesis submitted to Univ. of California, Berkeley, CA (US); TH: Thesis (Ph.D.); PBD: Aug 1996
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; 99 MATHEMATICS, COMPUTERS, INFORMATION SCIENCE, MANAGEMENT, LAW, MISCELLANEOUS; MOLECULES; Q CODES; WATER; VIBRATIONAL STATES; CARBON; MONTE CARLO METHOD; QUANTUM MECHANICS; THEORETICAL DATA; COMPUTERIZED SIMULATION; PARALLEL PROCESSING

Citation Formats

Brown, W R, and Lawrence Berkeley National Lab., CA. Quantum Monte Carlo for vibrating molecules. United States: N. p., 1996. Web. doi:10.2172/414375.
Brown, W R, & Lawrence Berkeley National Lab., CA. Quantum Monte Carlo for vibrating molecules. United States. https://doi.org/10.2172/414375
Brown, W R, and Lawrence Berkeley National Lab., CA. 1996. "Quantum Monte Carlo for vibrating molecules". United States. https://doi.org/10.2172/414375. https://www.osti.gov/servlets/purl/414375.
@article{osti_414375,
title = {Quantum Monte Carlo for vibrating molecules},
author = {Brown, W R and Lawrence Berkeley National Lab., CA},
abstractNote = {Quantum Monte Carlo (QMC) has successfully computed the total electronic energies of atoms and molecules. The main goal of this work is to use correlation function quantum Monte Carlo (CFQMC) to compute the vibrational state energies of molecules given a potential energy surface (PES). In CFQMC, an ensemble of random walkers simulate the diffusion and branching processes of the imaginary-time time dependent Schroedinger equation in order to evaluate the matrix elements. The program QMCVIB was written to perform multi-state VMC and CFQMC calculations and employed for several calculations of the H{sub 2}O and C{sub 3} vibrational states, using 7 PES`s, 3 trial wavefunction forms, two methods of non-linear basis function parameter optimization, and on both serial and parallel computers. In order to construct accurate trial wavefunctions different wavefunctions forms were required for H{sub 2}O and C{sub 3}. In order to construct accurate trial wavefunctions for C{sub 3}, the non-linear parameters were optimized with respect to the sum of the energies of several low-lying vibrational states. In order to stabilize the statistical error estimates for C{sub 3} the Monte Carlo data was collected into blocks. Accurate vibrational state energies were computed using both serial and parallel QMCVIB programs. Comparison of vibrational state energies computed from the three C{sub 3} PES`s suggested that a non-linear equilibrium geometry PES is the most accurate and that discrete potential representations may be used to conveniently determine vibrational state energies.},
doi = {10.2172/414375},
url = {https://www.osti.gov/biblio/414375}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Aug 01 00:00:00 EDT 1996},
month = {Thu Aug 01 00:00:00 EDT 1996}
}