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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
External coupled-cluster perturbation theory: description and application to weakly interaction dimers. Corrections
1Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, Florida 32611-8435, USA. lotrich@qtp.ufl.edu
The Journal of Chemical Physics
|May 17, 2011
Summary
External coupled-cluster perturbation theory (xCCPT) offers a flexible framework for developing new approximations. This method accurately predicts binding energies for Ne(2) and Ar(2) dimers, improving upon traditional coupled-cluster doubles approximations.
Area of Science:
- Quantum Chemistry
- Computational Physics
- Theoretical Chemistry
Background:
- Perturbation theory is crucial for developing accurate computational chemistry methods.
- Coupled-cluster approximations are widely used but can be computationally expensive.
- Developing efficient and accurate theoretical models for molecular interactions is an ongoing challenge.
Purpose of the Study:
- To present a unified formalism for perturbation theory using arbitrary external amplitudes: external coupled-cluster perturbation theory (xCCPT).
- To investigate the performance of xCCPT for weakly interacting dimers like Ne(2) and Ar(2) using various coupled-cluster doubles approximations.
- To explore the impact of different initial amplitude sets on the accuracy of perturbation calculations.
Main Methods:
- Development of the external coupled-cluster perturbation theory (xCCPT) formalism, accommodating nonperturbative approaches.
- Application of xCCPT with second-order corrections to Ne(2) and Ar(2) dimers.
- Utilizing various ring-coupled-cluster doubles (CCD) approximations, including direct-ring and antisymmetrized variants.
- Employing Coulomb attenuation via random phase approximation for initial amplitude selection.
Main Results:
- Ring-CCD approximations yielded poor interaction energies for Ne(2) and Ar(2).
- xCCPT corrections significantly improved binding energy predictions, achieving results within a few percent of coupled-cluster single double (triple) values for direct ring-CCD variants.
- Using MP2 amplitudes (neglecting exchange) as the initial term led to highly accurate Ne(2) and Ar(2) potentials.
- Accurate Na(2) potential calculation required a different initial wavefunction and perturbation, highlighting the importance of optimal amplitude selection.
Conclusions:
- The xCCPT approach provides a robust framework for improving perturbation theory calculations.
- The choice of initial amplitudes critically influences the accuracy of the perturbation expansion.
- An optimal set of external amplitudes can minimize perturbational effects, enhancing the predictability of computational methods for molecular interactions.
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