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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Published on: April 8, 2020

An adaptive coupled-cluster theory: @CC approach.

Dmitry I Lyakh¹, Rodney J Bartlett

¹Quantum Theory Project, University of Florida, Gainesville, Florida 32611, USA. liakh@qtp.ufl.edu

The Journal of Chemical Physics

|January 5, 2011

Summary

This study introduces an adaptive coupled-cluster theory that accurately describes electronic systems. The "black-box" method achieves high accuracy for single- and multireference phenomena using a compact set of cluster amplitudes.

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Area of Science:

Quantum chemistry
Computational physics
Theoretical chemistry

Background:

Coupled-cluster theory is a powerful quantum chemical method for describing electronic structure.
Accurately describing systems with strong multireference character remains a challenge.
Existing methods may require significant computational resources or manual tuning.

Purpose of the Study:

To present a novel adaptive coupled-cluster (CC) theory formulation.
To develop a method that automatically adjusts to various electronic system states.
To achieve convergence to the full configuration interaction (CI) limit for accurate electronic structure calculations.

Main Methods:

An adaptive formulation of coupled-cluster theory is developed.
Adaptivity is achieved through a guided selection of a compact set of cluster amplitudes.
A special importance-selection function (discriminatory function) is introduced for variable selection.

Main Results:

The adaptive CC method successfully describes both single- and multireference phenomena.
The approach demonstrates "black-box" usability, requiring minimal user intervention.
Tests on molecules with strong multireference character show excellent agreement with full CI results.
The method achieves chemical accuracy (mHartee accuracy) with a compact set of amplitudes.

Conclusions:

The presented adaptive coupled-cluster theory offers a robust and efficient approach for electronic structure calculations.
This method is capable of accurately describing complex electronic systems, including those with strong multireference character.
The "black-box" nature and accuracy make it a valuable tool for computational chemistry and physics.