Quantum Monte Carlo for vibrating molecules

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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, ... continued below

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137 p.

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Brown, W.R. August 1, 1996.

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  • Brown, W.R. Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

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Description

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.

Physical Description

137 p.

Notes

INIS; OSTI as DE97001595

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  • Other Information: DN: Thesis submitted to Univ. of California, Berkeley, CA (US); TH: Thesis (Ph.D.)

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  • Other: DE97001595
  • Report No.: LBNL--39574
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/414375 | External Link
  • Office of Scientific & Technical Information Report Number: 414375
  • Archival Resource Key: ark:/67531/metadc677637

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  • August 1, 1996

Added to The UNT Digital Library

  • July 25, 2015, 2:20 a.m.

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  • April 5, 2016, 5:53 p.m.

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Brown, W.R. Quantum Monte Carlo for vibrating molecules, report, August 1, 1996; California. (digital.library.unt.edu/ark:/67531/metadc677637/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.