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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Multireference Fock space coupled cluster method in the effective and intermediate Hamiltonian formulation for the
1Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland. musial@ich.us.edu.pl
The Journal of Chemical Physics
|April 10, 2012
Summary
A new computational chemistry method, Intermediate Hamiltonian Fock Space Coupled Cluster (IH-FS-CCSD), accurately models double electron attachment. This efficient approach provides results comparable to CCSDT methods for potential energy curves and excitation spectra.
Area of Science:
- Quantum Chemistry
- Computational Physics
Background:
- Coupled Cluster (CC) methods are essential for accurate electronic structure calculations.
- Fock Space (FS) CC methods are used for studying electron attachment and detachment processes.
- Existing methods can be computationally intensive or lack rigorous size-extensivity.
Purpose of the Study:
- To formulate and implement an Intermediate Hamiltonian (IH) based multireference Coupled Cluster (CC) method within the double electron attached (2,0) sector of Fock Space (FS).
- To develop a computationally efficient and size-extensive method for calculating properties related to double electron attachment.
- To assess the performance of the new method against established techniques.
Main Methods:
- Formulation of the Intermediate Hamiltonian (IH) multireference Coupled Cluster (CC) method.
- Implementation within the double electron attached (2,0) sector of Fock Space (FS).
- Replacement of iterative schemes with matrix diagonalization for the (2,0) FS-CC equations.
Main Results:
- The developed IH-FS-CCSD (2,0) method is rigorously size-extensive, easy to implement, and numerically efficient.
- Results obtained are comparable or superior to equation-of-motion coupled cluster methods at the CCSDT level.
- The method successfully calculates potential energy curves for systems like the Na(2) dimer and provides smooth potential energy curves for twisted ethylene.
Conclusions:
- The IH-FS-CCSD (2,0) method offers a robust and efficient approach for studying double electron attachment phenomena.
- This method is valuable for determining excitation spectra in challenging cases, such as the carbon atom.
- The technique provides smooth, cusp-free potential energy curves, enhancing its utility in molecular modeling.
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