Taming the First-Row Diatomics: A Full Configuration Interaction Quantum Monte Carlo Study.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Stochastic electronic structure methods are crucial for accurate molecular energy calculations.
• The initiator full configuration interaction quantum Monte Carlo (i-FCIQMC) is a novel, highly accurate technique.
• Accurate calculation of dissociation energies for diatomic molecules remains a challenge.

Purpose of the Study:

• To apply the i-FCIQMC method to a series of challenging first-row diatomic molecules.
• To assess the accuracy and efficiency of i-FCIQMC for calculating dissociation energies.
• To investigate the nature of static correlation in these systems using i-FCIQMC wave functions.

Main Methods:

• Utilizing the initiator full configuration interaction quantum Monte Carlo (i-FCIQMC) method.
• Performing calculations on Be2, C2, CN, CO, N2, NO, O2, and F2.
• Analyzing the size consistency and wave function properties of i-FCIQMC.

Main Results:

• i-FCIQMC accurately determined dissociation energies for the studied diatomics, achieving chemical accuracy.
• Calculations were performed in a black-box manner, requiring no prior wave function specification.
• Size consistency was demonstrated for stretched molecular geometries.
• Dominant determinants contributing to static correlation were dynamically identified, providing algorithmic and chemical insights.

Conclusions:

• The i-FCIQMC method is a powerful and accurate tool for electronic structure calculations of molecules.
• It provides chemically accurate dissociation energies for challenging diatomic systems.
• The method offers insights into static correlation and the underlying electronic structure.