scholarly journals Molecular Properties by Quantum Monte Carlo: An Investigation on the Role of the Wave Function Ansatz and the Basis Set in the Water Molecule

2013 ◽  
Vol 9 (10) ◽  
pp. 4332-4350 ◽  
Author(s):  
Andrea Zen ◽  
Ye Luo ◽  
Sandro Sorella ◽  
Leonardo Guidoni
Keyword(s):  
Monte Carlo ◽  
Wave Function ◽  
Water Molecule ◽  
Quantum Monte Carlo ◽  
Molecular Properties ◽  
Basis Set

scholarly journals Diffusion and Reptation Quantum Monte Carlo Study of the NaK Molecule

2018 ◽  
Author(s):  
Marc E. Segovia ◽  
Oscar Ventura
Keyword(s):  
Monte Carlo ◽  
Dipole Moment ◽  
Potential Energy ◽  
Dissociation Energy ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Basis Set ◽  
Energy Curve ◽  
Dft Methods ◽  
Trial Wavefunction

<p>Diffusion Monte Carlo (DMC) and Reptation Monte Carlo (RMC) methods, have been applied to study some properties of the NaK molecule. Hartree-Fock (HF), Density Functional (DFT) and single and double configuration interaction (SDCI) wavefunctions with a valence quadruple zeta atomic natural orbital (VQZ/ANO) basis set were used as trial wavefunctions. Values for the potential energy curve, dissociation energy and dipole moment were calculated for all methods and compared with experimental results and previous theoretical derivations. Quantum Monte Carlo (QMC) calculations were shown to be useful methods to recover correlation in NaK, essential to obtain a reasonable description of the molecule. The equilibrium distance—interpolated from the potential energy curves—yield a value of 3.5 Å, in agreement with the experimental value. The dissociation energy, however, is not as good. In this case, a conventional CCSD(T) calculation with an extended aug-pc-4 basis set gives a much better agreement to experiment. On the contrary, the CCSD(T), other MO and DFT methods are not able to reproduce correctly the large dipole moment of this molecule. Even DMC methods with a simple HF trial wavefunction are able to give a better agreement to experiment. RMC methods are even better, and the value obtained with a B3LYP trial wavefunction is very close to the experimental one.</p>

scholarly journals Unconventional phase transitions in strongly anisotropic 2D (pseudo)spin systems

2018 ◽  
Vol 185 ◽  
pp. 08006
Author(s):  
Vitaly Konev ◽  
Evgeny Vasinovich ◽  
Vasily Ulitko ◽  
Yury Panov ◽  
Alexander Moskvin
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Phase Transitions ◽  
Ground State ◽  
Quantum Monte Carlo ◽  
Mean Field ◽  
Spin Systems ◽  
Field Approach ◽  
Generalized Mean

We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S = 1 (pseudo)spin system to find the ground state phase with its evolution under application of the (pseudo)magnetic field. The comparison of the two methods allows us to clearly demonstrate the role of quantum effects. Special attention is given to the role played by an effective single-ion anisotropy ("on-site correlation").

scholarly journals OPTIMIZATION OF QUANTUM MONTE CARLO WAVE FUNCTION: STEEPEST DESCENT METHOD

2010 ◽  
Vol 21 (04) ◽  
pp. 523-533 ◽  
Author(s):  
M. EBRAHIM FOULAADVAND ◽  
MOHAMMAD ZARENIA
Keyword(s):  
Monte Carlo ◽  
Wave Function ◽  
Quantum Monte Carlo ◽  
Descent Method ◽  
Steepest Descent ◽  
Steepest Descent Method ◽  
Direct Energy Minimization ◽  
Direct Energy ◽  
Spatial Coordinates ◽  
Quantum Monte Carlo Method

We have employed the steepest descent method to optimize the variational groundstate quantum Monte Carlo wave function for He , Li , Be , B and C atoms. We have used both the direct energy minimization and the variance minimization approaches. Our calculations show that in spite of receiving insufficient attention, the steepest descent method can successfully minimize the wave function. All the derivatives of the trial wave function respect to spatial coordinates and variational parameters have been computed analytically. Our groundstate energies are in a very good agreement with those obtained with diffusion quantum Monte Carlo method (DMC) and the exact results.

scholarly journals Role of winding numbers in quantum Monte Carlo simulations

1998 ◽  
Vol 57 (21) ◽  
pp. 13382-13385 ◽  
Author(s):  
Patrik Henelius ◽  
S. M. Girvin ◽  
Anders W. Sandvik
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Quantum Monte Carlo ◽  
Quantum Monte Carlo Simulations

Optimization of a multideterminant wave function for quantum Monte Carlo: Li2 (X 1Σ+g)

1992 ◽  
Vol 96 (3) ◽  
pp. 2422-2423 ◽  
Author(s):  
Zhiwei Sun ◽  
Robert N. Barnett ◽  
William A. Lester
Keyword(s):  
Monte Carlo ◽  
Wave Function ◽  
Quantum Monte Carlo
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