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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Correction to constrained coupled cluster doubles models based on the second coupled cluster central moment.

David W Small¹, Martin Head-Gordon

¹Department of Chemistry, University of California, Berkeley, California 94720, USA.

The Journal of Chemical Physics

|August 21, 2007

Summary

We introduce a correction for the perfect pairing (PP) coupled cluster model. This method recovers significant missing correlation energy in active-space calculations, improving accuracy for quantum chemistry simulations.

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Area of Science:

Quantum Chemistry
Computational Chemistry
Theoretical Chemistry

Background:

Coupled cluster methods are essential for accurate electronic structure calculations.
The perfect pairing (PP) model offers a computationally efficient approximation.
However, the PP model neglects significant electron correlation, limiting its accuracy.

Purpose of the Study:

To develop a correction to the perfect pairing (PP) coupled cluster model.
To improve the accuracy of PP calculations, particularly for active-space problems.
To recover missing correlation energy in quantum chemical computations.

Main Methods:

A correction is developed for the coupled cluster version of the perfect pairing (PP) model.
Modified PP amplitudes are determined by vanishing the second coupled cluster central moment.
The deviation between modified and unmodified PP amplitudes is minimized.

Main Results:

The developed correction successfully recovers a substantial portion of the missing active-space coupled cluster singles and doubles correlation energy.
Numerical results demonstrate the effectiveness of the proposed correction.
The correction shows potential for generalization to other constrained doubles models.

Conclusions:

The proposed correction enhances the accuracy of the perfect pairing model for quantum chemistry.
This approach improves the recovery of electron correlation energy in active-space calculations.
The method offers a valuable tool for more precise electronic structure predictions.