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The mathematical expression known as the wave function, ψ, contains information about each orbital and the wavelike properties of electrons in an isolated atom. When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes. This process of combining the wave functions for atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals. The new orbitals that...

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Published on: April 8, 2020

Nonvariational Orbital Optimization Techniques for the AP1roG Wave Function.

Katharina Boguslawski¹, Paweł Tecmer¹, Patrick Bultinck²

¹Department of Chemistry and Chemical Biology, McMaster University , 1280 Main Street West, Hamilton, L8S 4M1 Ontario, Canada.

Journal of Chemical Theory and Computation

|November 20, 2015

Summary

This summary is machine-generated.

New orbital optimization methods for antisymmetric product of one-reference orbital geminal (AP1roG) wave functions offer more robust and less stringent approximations than previous approaches. These methods improve calculations for complex multireference chemical problems.

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Area of Science:

Quantum Chemistry
Computational Chemistry
Theoretical Chemistry

Background:

The antisymmetric product of one-reference orbital geminal (AP1roG) wave function, also known as pair-coupled cluster doubles, is a powerful method for describing electron correlation.
Existing orbital optimization schemes for AP1roG can be computationally demanding and may face convergence issues for challenging multireference systems.
The projected seniority-two (PS2-AP1roG) method offers an improvement but can still be limited in robustness.

Purpose of the Study:

To develop and introduce novel nonvariational orbital optimization schemes for the AP1roG wave function.
To provide more robust and less stringent approximations compared to the existing PS2-AP1roG method.
To assess the performance of these new methods on benchmark multireference systems.

Main Methods:

Development of new nonvariational orbital optimization schemes as extensions to the PS2-AP1roG method.
Implementation and application of these schemes to study challenging chemical phenomena.
Comparison of the new methods with the variational orbital optimization scheme and PS2-AP1roG.

Main Results:

The proposed orbital optimization schemes demonstrate improved robustness over the PS2-AP1roG method.
These new methods provide less stringent approximations to the variational orbital optimization scheme.
Successful application to multireference problems including Be insertion into H2, cyclobutadiene automerization, pyridyne stability, and benzene aromaticity.

Conclusions:

The newly developed nonvariational orbital optimization schemes offer a more practical and reliable approach for AP1roG calculations.
These methods enhance the applicability of AP1roG to a wider range of complex chemical systems.
The findings pave the way for more accurate theoretical studies of challenging electronic structures.