Calculating potential energy curves with fixed-node diffusion Monte Carlo: CO and N₂.

Area of Science:

• Computational chemistry
• Quantum mechanics
• Materials science

Background:

• Accurate electronic structure calculations are crucial for understanding molecular behavior.
• Conventional high-accuracy methods face computational scaling challenges with increasing system size.
• Quantum Monte Carlo (QMC) offers a potential alternative with favorable scaling properties.

Purpose of the Study:

• To evaluate the feasibility of routine Quantum Monte Carlo (QMC) application for electronic structure problems.
• To generate highly accurate Born-Oppenheimer potential energy curves (PECs) for small molecular systems using fixed-node Diffusion Monte Carlo (DMC).
• To compare DMC-derived PECs with established high-accuracy methods and empirical data.

Main Methods:

• Application of fixed-node Diffusion Monte Carlo (DMC) to calculate PECs.
• Utilized multiconfigurational trial wavefunctions within the DMC framework.
• Tested on the singlet ground electronic states of carbon monoxide (CO) and nitrogen (N₂).
• Compared results with multireference configuration interaction and empirical spectroscopic data.

Main Results:

• DMC-derived PECs closely agreed with benchmark data.
• Observed n³ scaling with electron number, a significant improvement over conventional methods (n⁷ or worse).
• Current computational cost for small systems remains high due to a large pre-factor.

Conclusions:

• Fixed-node DMC is a robust and reliable method for generating accurate molecular PECs.
• QMC methods exhibit advantageous scaling for larger systems, despite current computational intensity for small molecules.
• QMC's suitability for parallelization positions it as a key method for future high-performance computing architectures.