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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Published on: April 8, 2020

Block correlated coupled cluster method with a complete-active-space self-consistent-field reference function: the

Tao Fang¹, Jun Shen, Shuhua Li

¹Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, People's Republic of China.

The Journal of Chemical Physics

|December 24, 2008

Summary

This summary is machine-generated.

A new method, Complete Active Space Block Correlated Coupled Cluster (CAS-BCCC4), accurately calculates electronic excited states. This computational chemistry advancement provides reliable excitation energies for various molecules.

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Area of Science:

Quantum Chemistry
Computational Chemistry
Theoretical Chemistry

Background:

Accurate calculation of electronic excited states is crucial for understanding molecular properties and reactions.
Existing methods face challenges in balancing accuracy and computational cost for excited-state calculations.

Purpose of the Study:

To generalize the Block Correlated Coupled Cluster (BCCC) theory for low-lying electronic excited states.
To develop and implement an efficient CAS-BCCC4 method for excited-state investigations.

Main Methods:

Generalization of CAS-BCCC theory for excited states.
Truncation of the cluster operator to the four-block correlation level (CAS-BCCC4).
Application to study potential energy surfaces and excitation energies of small molecules.

Main Results:

Efficient implementation of the CAS-BCCC4 method.
Accurate calculation of excited-state potential energy surfaces for HF and C2.
Reliable evaluation of adiabatic and vertical excitation energies for CH2, N2, and trans-1,3-butadiene.
Comparison with high-level theoretical methods (FCI, ICM RCI, CASPT2) shows excellent agreement.

Conclusions:

The CAS-BCCC4 approach provides high accuracy for low-lying excited states.
This method offers a computationally efficient and accurate tool for excited-state electronic structure calculations.