Second-order state-specific multireference Møller-Plesset perturbation theory (SS-MRMPPT) applied to geometry...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate computation of molecular geometries is crucial in chemistry.
• Existing methods may struggle with diverse electronic structures, including radicals and charged species.
• Second-order state-specific multireference Møller-Plesset perturbation theory (SS-MRMPPT) offers a potential solution.

Purpose of the Study:

• To test and validate a numerically oriented gradient scheme for SS-MRMPPT.
• To assess the performance of this scheme in calculating geometrical parameters (bond lengths, angles).
• To demonstrate the first systematic application of the SS-MRMPPT numerical gradient approach.

Main Methods:

• Implementation of a numerically oriented gradient scheme for SS-MRMPPT.
• Calculation of geometrical parameters for various molecular systems (e.g., H2O, O3, N2H2, C2H4, C2H2F2, 1,3-butadiene, cyclobutadiene, 2,6-pyridynium cation).
• Comparison of results with existing theoretical and experimental data.

Main Results:

• The SS-MRMPPT gradient scheme was successfully implemented and validated.
• Accurate geometrical parameters were computed for a diverse range of molecules, including neutral, charged, closed-shell, and open-shell systems.
• The computational results showed good agreement with previously reported theoretical and experimental data.

Conclusions:

• The SS-MRMPPT gradient scheme demonstrates substantial potential for calculating geometrical parameters.
• This method is reliable for diverse molecular systems, including radicals and perturbed species.
• This work represents the first systematic application of the SS-MRMPPT numerical gradient approach.