Interpair electron correlation by second-order perturbative corrections to PNOF5

Area of Science:

• Quantum chemistry
• Computational physics
• Theoretical chemistry

Background:

• Piris natural orbital functional 5 (PNOF5) is a method for electronic structure calculations.
• Second-order corrections are needed to improve the accuracy of approximate quantum chemical methods.

Purpose of the Study:

• To derive and implement second-order corrections to PNOF5 using size-consistent second-order multiconfigurational perturbation theory (SC2-MCPT).
• To propose a modified SC2-MCPT approach for improved description of dispersion interactions and molecular dissociation.

Main Methods:

• Utilizing an antisymmetrized product of strongly orthogonal geminals for PNOF5.
• Implementing SC2-MCPT with explicit expansion coefficients based on occupation numbers.
• Developing a modified SC2-MCPT focusing on doubly excited determinants from different geminals.

Main Results:

• The SC2-MCPT formulation provides accurate second-order corrections to PNOF5.
• The modified SC2-MCPT successfully describes dispersion interactions in the helium dimer.
• The method avoids curve breakdown in homolytic dissociations of FH, CO, and N2.

Conclusions:

• The developed SC2-MCPT method offers significant improvements over standard PNOF5.
• The formulation accurately predicts molecular properties, demonstrating its potential for computational chemistry applications.