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Towards the multireference Brillouin-Wigner coupled-clusters method with iterative connected triples: MR
1J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 18223 Prague 8, Czech Republic. jiri.pittner@jh-inst.cas.cz
The Journal of Chemical Physics
|May 28, 2005
Summary
Researchers developed an advanced quantum chemistry method, MRBWCCSDT-alpha, for accurate molecular state calculations. This new approach improves the prediction of electronic states for molecules like oxygen.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Accurate prediction of molecular electronic states is crucial for understanding chemical reactions and properties.
- Existing multireference coupled-cluster methods have limitations in handling general reference configurations and accuracy.
Purpose of the Study:
- To develop and implement an approximation of the state-specific Brillouin-Wigner coupled-cluster method with singles, doubles, and triples (MRBWCCSDT-alpha).
- To assess the accuracy of the MRBWCCSDT-alpha method for calculating electronic states of the oxygen molecule.
- To evaluate the size-extensivity of the developed method.
Main Methods:
- Development and implementation of the MRBWCCSDT-alpha method, an approximation for multireference Brillouin-Wigner coupled-cluster with singles, doubles, and triples.
- Application of the method to calculate the X3sigma(g-), a1delta(g), and b1sigma(g+) states of the oxygen molecule.
- Comparison of MRBWCCSDT-alpha results with previous MRBWCCSD, doubly ionized similarity transformed equation-of-motion CCSD, multireference configuration interaction, and experimental data.
- Performance of explicit tests for the size-extensivity of the MRBWCCSDT-alpha method with iterative correction.
Main Results:
- The MRBWCCSDT-alpha method was successfully developed and implemented for general reference configurations.
- Calculations on oxygen molecule states showed good agreement with experimental data and other high-level theoretical methods.
- The accuracy of the multireference treatment was validated through comparisons.
Conclusions:
- The MRBWCCSDT-alpha method provides an accurate and reliable approach for multireference electronic structure calculations.
- The method demonstrates good performance for open-shell systems, as exemplified by the oxygen molecule.
- The developed method advances the capabilities of quantum chemical calculations for complex molecular systems.