Quantum Monte Carlo for vibrating molecules

Technical Report · Thu Aug 01 04:00:00 EDT 1996

DOI:https://doi.org/10.2172/414375· OSTI ID:414375

Brown, W R ^[1]

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1. Univ. of California, Berkeley, CA (United States). Chemistry Dept.

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.

• Research Organization: Lawrence Berkeley National Lab., CA (United States)
• Sponsoring Organization: USDOE Office of Energy Research, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 414375
• Report Number(s): LBNL--39574; ON: DE97001595
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
99 GENERAL AND MISCELLANEOUS
CARBON
COMPUTERIZED SIMULATION
MOLECULES
MONTE CARLO METHOD
PARALLEL PROCESSING
Q CODES
QUANTUM MECHANICS
THEORETICAL DATA
VIBRATIONAL STATES
WATER