Generalized valence bond wave functions in quantum Monte Carlo.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Electronic Structure Theory

Background:

• Accurate calculation of electronic energy differences is crucial in chemistry.
• Static and dynamic electron correlation present significant challenges for computational methods.
• Generalized Valence Bond (GVB) offers an intuitive way to model static correlation.

Purpose of the Study:

• To develop a robust quantum Monte Carlo (QMC) method for high-accuracy energy difference calculations.
• To integrate GVB wave functions with diffusion QMC for comprehensive correlation treatment.
• To demonstrate the method's efficiency and accuracy across various chemical systems.

Main Methods:

• Utilizing generalized valence bond (GVB) wave functions to capture static correlation.
• Employing modified Walker branching and Jastrow factors for diffusion QMC.
• Applying the combined GVB-QMC approach to selected chemical problems.

Main Results:

• Achieved accuracy within a few tenths of a kcal/mol for energy differences.
• Successfully computed singlet-triplet splittings in methylene and ethylene.
• Demonstrated accuracy for 2+2 cycloaddition reactions and Be(2) bond breaking.

Conclusions:

• The presented GVB-QMC technique provides a reliable and accurate approach for electronic energy calculations.
• This method effectively incorporates both static and dynamic electron correlation.
• The demonstrated accuracy highlights its potential for diverse chemical applications.