Analytic Energy Gradients and Spin Multiplicities for Orbital-Optimized Second-Order Perturbation Theory with...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Standard second-order Møller-Plesset perturbation theory (MP2) can be computationally expensive and unreliable for certain chemical systems.
• Orbital-optimized MP2 with the resolution of the identity approach (OO-RI-MP2) offers improvements but can still be resource-intensive for gradient calculations.

Purpose of the Study:

• To present an efficient implementation of analytic energy gradients and spin multiplicities for density-fitted orbital-optimized second-order perturbation theory (DF-OMP2).
• To compare the computational cost and accuracy of DF-OMP2 with existing methods like OO-RI-MP2 and standard MP2.

Main Methods:

• Implementation of analytic energy gradients and spin multiplicities for DF-OMP2.
• Application of DF-OMP2 to alkanes, conjugated dienes, and noncovalent interaction complexes.
• Comparison of computational costs for single-point analytic gradient computations against OO-RI-MP2.
• Evaluation of aromatic bond dissociation energies using DF-OMP2 and MP2.

Main Results:

• DF-OMP2 analytic gradients are substantially less computationally expensive than OO-RI-MP2, with costs being 9-11 times lower on average.
• DF-OMP2 shows significantly improved performance for aromatic bond dissociation energies compared to MP2, with a mean absolute error of 2.5 kcal mol(-1) versus 22.6 kcal mol(-1).
• The method demonstrates superior accuracy and robustness for electronically challenging systems.

Conclusions:

• DF-OMP2 provides a more computationally efficient and accurate alternative to standard MP2 and OO-RI-MP2 for calculating analytic gradients.
• The method is particularly beneficial for systems where standard MP2 is unreliable, such as free radicals.
• DF-OMP2 is recommended as a robust method with the same computational scaling as canonical MP2 for problematic systems.