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Guo S, Bajdich M, Mitas L, Reynolds PJ. Study of dipole moments of LiSr and KRb molecules by quantum Monte Carlo methods. Mol Phys 2013. [DOI: 10.1080/00268976.2013.788741] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Shi Guo
- a Department of Physics , North Carolina State University , Raleigh , NA , 27695
| | - Michal Bajdich
- b Joint Center for Artificial Photosynthesis, Lawrence Berkeley Laboratory, Department of Chemical and Biomolecular Engineering , University of California , Berkeley , CA , 94720
| | - Lubos Mitas
- a Department of Physics , North Carolina State University , Raleigh , NA , 27695
| | - Peter J. Reynolds
- a Department of Physics , North Carolina State University , Raleigh , NA , 27695
- c Physics Division and Physical Sciences Directorate, Army Research Office , Research Triangle Park, NC , 27703
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Lu SI. A diffusion quantum Monte Carlo study on the lowest singlet and triplet electronic states of BN molecule. J Chem Phys 2005; 123:174313. [PMID: 16375534 DOI: 10.1063/1.2104347] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Ab initio calculation of both the lowest singlet and triplet electronic states of BN has been performed by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo method with the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculation gives equilibrium bond lengths and equilibrium harmonic frequencies of 1.3317(7) A and 1529(7) cm(-1), respectively, for the lowest triplet state and 1.2751(7) A and 1709(8) cm(-1), respectively, for the lowest singlet state. Also, the Monte Carlo calculation reports an energy separation of 178(83) cm(-1) between the two electronic states and recommends the ground state is the lowest triplet state.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. Accuracy of a random-walk-based approach in the determination of equilibrium bond lengths and harmonic frequencies for some doublet first-row diatomic radicals. J Chem Phys 2005; 123:074104. [PMID: 16229556 DOI: 10.1063/1.1996578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The accuracy of equilibrium bond lengths and harmonic frequencies for 12 doublet first-row diatomic radicals is presented as predicted by the fixed-node diffusion quantum Monte Carlo method based on the Ornstein-Uhlenbeck random walk guided by the floating spherical Gaussian orbital and spherical Gaussian geminal-type trial wave function. Compared to the experimental determined values, the random-walk-based approach gives the absolute mean deviations of 0.0019 A and 18 cm-1 for the equilibrium bond length and harmonic frequency, respectively. We also compare the random-walk-based results with some coupled-cluster-based values.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. Theoretical study of transition state structure and reaction enthalpy of the F+H2→HF+H reaction by a diffusion quantum Monte Carlo approach. J Chem Phys 2005; 122:194323. [PMID: 16161589 DOI: 10.1063/1.1899125] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Ab initio calculations of transition state structure and reaction enthalpy of the F + H2-->HF + H reaction has been carried out by the fixed-node diffusion quantum Monte Carlo method in this study. The Monte Carlo sampling is based on the Ornstein-Uhlenbeck random walks guided by a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculated barrier height of 1.09(16) kcal/mol is consistent with the experimental values, 0.86(10)/1.18(10) kcal/mol, and the calculated value from the multireference-type coupled-cluster (MRCC) calculation with the aug-cc-pVQZ(F)/cc-pVQZ(H) basis set, 1.11 kcal/mol. The Monte Carlo-based calculation also gives a similar value of the reaction enthalpy, -32.00(4) kcal/mol, compared with the experimental value, -32.06(17) kcal/mol, and the calculated value from a MRCC/aug-cc-pVQZ(F)/cc-pVQZ(H) calculation, -31.94 kcal/mol. This study clearly indicates a further application of the random-walk-based approach in the field of quantum chemical calculation.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. Electron affinities with diffusion quantum Monte Carlo for C2 and BO molecules. J Chem Phys 2004; 121:10495-7. [PMID: 15549931 DOI: 10.1063/1.1811610] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
To verify the performance of the fixed-node diffusion quantum Monte Carlo method in electron affinities calculations, the adiabatic electron affinities of C(2) and BO molecules calculated by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo simulations guiding by trial wave functions constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals are presented in this work. The random walk based results, 3.264(43) and 2.507(32) eV for C(2) and BO, respectively, are compared with the available best experimental determined values, 3.269(6) and 2.508(8) eV for C(2) and BO, respectively, and the results of other theoretical calculations.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien 831, Taiwan.
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Lu SI. The accuracy of diffusion quantum Monte Carlo simulations in the determination of molecular equilibrium structures. J Chem Phys 2004; 121:10365-9. [PMID: 15549914 DOI: 10.1063/1.1809599] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
For a test set of 17 first-row small molecules, the equilibrium structures are calculated with Ornstein-Uhlenbeck diffusion quantum Monte Carlo simulations guiding by trial wave functions constructed from floating spherical Gaussian orbitals and spherical Gaussian geminals. To measure performance of the Monte Carlo calculations, the mean deviation, the mean absolute deviation, the maximum absolute deviation, and the standard deviation of Monte Carlo calculated equilibrium structures with respect to empirical equilibrium structures are given. This approach is found to yield results having a uniformly high quality, being consistent with empirical equilibrium structures and surpassing calculated values from the coupled cluster model with single, double, and noniterative triple excitations [CCSD(T)] with the basis sets of cc-pCVQZ and cc-pVQZ. The nonrelativistic equilibrium atomization energies are also presented to assess performance of the calculated methods. The mean absolute deviations regarding experimental atomization energy are 0.16 and 0.21 kcal/mol for the Monte Carlo and CCSD(T)/cc-pCV(56)Z calculations, respectively.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien 831, Taiwan.
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Lu SI. Random walks based approach to study on molecular structures and torsional barrier heights of hydrogen peroxide. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2004.06.142] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Lu SI. Diffusion quantum Monte Carlo for equilibrium structures and harmonic frequencies of ethane and ozone molecules. J Chem Phys 2004; 120:10423-5. [PMID: 15268070 DOI: 10.1063/1.1738114] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Application of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method in combination with a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals to studies on the equilibrium structures and harmonic frequencies of ethane and ozone is presented. These Monte Carlo computed results are compared with those of experiments as well as the coupled cluster methods with the correlation consistent basis sets for the two molecules. For ozone, we also compare the Monte Carlo results with the results from multireference calculations.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. Ornstein–Uhlenbeck diffusion quantum Monte Carlo study on the bond lengths and harmonic frequencies of some first-row diatomic molecules. J Chem Phys 2004; 120:3185-8. [PMID: 15268471 DOI: 10.1063/1.1639370] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This article accesses the performance of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo with regard to the calculation of molecular geometries and harmonic frequencies of H2, LiH, HF, Li2, LiF, CO, N2, and F2 molecules. A comparison of the results for the eight first-row diatomic molecules from experiments, CCSD(T)/6-311G(3df,3pd) and CCSD(T)/cc-pV5Z levels of theory as well as our work is given. The results presented show that quantum Monte Carlo is becoming powerful tools for ab initio electronic structure calculations.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. A diffusion quantum Monte Carlo study of geometries and harmonic frequencies of molecules. J Chem Phys 2004; 120:14-7. [PMID: 15267255 DOI: 10.1063/1.1630022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This article describes an approach in determination of equilibrium geometries and harmonic frequencies of molecules by the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method based on the floating spherical Gaussians. In conjunction with a projected and renormalized Hellmann-Feynman gradient and an electronic energy at variational Monte Carlo and diffusion quantum Monte Carlo, respectively, the quasi-Newton algorithm implemented with the Broyden-Fletcher-Goldfarb-Shanno updated Hessian was used to find the optimized molecular geometry. We applied this approach to N2 and H2O molecules. The geometry and harmonic frequencies calculated were consistent with some sophisticated ab initio calculated values within reasonable statistical uncertainty.
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Affiliation(s)
- Shih-I Lu
- Department of Applied Chemistry, Fooyin University, 151 Chinhsueh Road, Ta-Liao Hsiang, Kaohsiung Hsien, 831 Taiwan.
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Lu SI. Accurate atomization energies and dipole moments from Ornstein–Uhlenbeck diffusion quantum Monte Carlo calculations for small first-row polyatomic molecules. J Chem Phys 2003. [DOI: 10.1063/1.1570813] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Lu SI. Performance of Ornstein–Uhlenbeck diffusion quantum Monte Carlo for first-row diatomic dissociation energies and dipole moments. J Chem Phys 2003. [DOI: 10.1063/1.1558472] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Lu SI. Ornstein–Uhlenbeck diffusion quantum Monte Carlo calculations on BH and HF with the floating spherical Gaussian orbitals and spherical Gaussian geminals. Chem Phys 2003. [DOI: 10.1016/s0301-0104(02)00957-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Casalegno M, Mella M, Rappe AM. Computing accurate forces in quantum Monte Carlo using Pulay’s corrections and energy minimization. J Chem Phys 2003. [DOI: 10.1063/1.1562605] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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