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Related Experiment Video

Updated: May 23, 2026

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Published on: April 8, 2020

Approaching chemical accuracy with quantum Monte Carlo.

F R Petruzielo¹, Julien Toulouse, C J Umrigar

¹Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA. frp3@cornell.edu

The Journal of Chemical Physics

|April 3, 2012

Summary

Quantum Monte Carlo methods accurately predict molecular atomization energies. Advanced wavefunctions, like complete active space Slater-Jastrow, achieve near chemical accuracy, crucial for computational chemistry.

Related Experiment Videos

Last Updated: May 23, 2026

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Published on: April 8, 2020

Area of Science:

Computational Chemistry
Quantum Mechanics
Theoretical Chemistry

Background:

Predicting molecular atomization energies is vital for chemical reaction understanding.
Quantum Monte Carlo (QMC) methods offer a powerful approach for high-accuracy electronic structure calculations.
Previous QMC studies have faced challenges in achieving chemical accuracy for larger molecular systems.

Purpose of the Study:

To investigate the accuracy of diffusion Monte Carlo (DMC) for calculating atomization energies of the G2 molecular set.
To assess the impact of basis set size and trial wavefunction complexity on QMC accuracy.
To determine if QMC can reach chemical accuracy (within 1 kcal/mol) for atomization energies.

Main Methods:

Utilized diffusion Monte Carlo (DMC) and variational Monte Carlo (VMC) methods.
Employed Slater-Jastrow trial wavefunctions constructed from Hartree-Fock orbitals.
Investigated basis set dependence and the effect of optimizing orbitals.
Explored the use of complete active space (CAS) Slater-Jastrow wavefunctions.

Main Results:

A single determinant Slater-Jastrow wavefunction with the largest basis set yielded a mean absolute deviation (MAD) of 3.0 kcal/mol from experimental atomization energies.
Optimizing orbitals with VMC reduced the MAD to 2.1 kcal/mol.
DMC with a small CAS Slater-Jastrow wavefunction achieved near chemical accuracy, with an MAD of 1.2 kcal/mol.
Calculations on phosphorus-containing systems indicated that larger active spaces further improve accuracy.

Conclusions:

QMC, particularly DMC with advanced wavefunctions, is highly effective for calculating molecular atomization energies.
Near chemical accuracy is achievable for the G2 set using a small CAS Slater-Jastrow wavefunction.
The accuracy of QMC methods can be systematically improved by increasing the complexity of the trial wavefunction, such as employing larger active spaces.