Inexpensive electron-pair methods to model ground and excited states across the periodic table
Katharina Boguslawski1,2
1 Faculty of Chemistry, Nicolaus Copernicus University in Torun, Poland
2 Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Torun, Poland
E-mail: k.boguslawski@fizyke.umk.pl
The correlation energy is a central quantity in quantum chemistry. It is usually defined as the error in the electronic energy calculated within the independent-particle model of Hartree-Fock theory with respect to the exact solution of the electronic Schr¨odinger equation. Although there exists no rigorous distinction between different types of electron correlation effects, the correlation energy is typically divided into two categories: static/nondynamic and dynamic. While dynamic electron correlation effects can be accurately described by standard, well-established methods, like Møller-Plesset perturbation theory or single-reference coupled cluster theory, present-day quantum chemistry lacks simple, robust, and efficient algorithms for a qualitatively correct description of stronglycorrelated many-body problems. We present a conceptually different approach that is well suited for strongly correlated electrons, but does not use the orbital model. Our method exploits the feature that electron correlation effects can be built into the many-electron wavefunction using two-electron functions, also called geminals. One of the simplest practical geminal approaches is the antisymmetric product of 1-reference-orbital geminals (AP1roG) [1, 2, 4], which is equivalent to the pair-Coupled-Cluster Doubles model [3].
In this work, we discuss the performance of AP1roG-based methods [3, 4, 5] in modeling electronic structures for molecules containing light and heavy elements, including actinides. We will present different excited state models [6, 7, 8] that allow us to target singly- and doubly-excited states with electron-pair theories. Our study indicates that geminal-based approaches provide a cheap, robust, and accurate alternative for the description of electron correlation effects in both ground and excited states.
References
[1] K. Boguslawski, P. Tecmer, P.W. Ayers, P. Bultinck, S. De Baerdemacker, D. Van Neck, Phys. Rev. B 89 (2014) 201106(R).
[2] K. Boguslawski, P. Tecmer, P. W. Ayers, P. Bultinck, S. De Baerdemacker, D. Van Neck, J. Chem. Theory Comput. 10 (2014) 4873.
[3] T. Henderson, I.W. Bulik, T. Stein, G.E. Scuseria, J. Chem. Phys. 141 (2014), 244104.
[4] K. Boguslawski, P. W. Ayers, J. Chem. Theory Comput. 11, (2015) 5252.
[5] K. Boguslawski, P. Tecmer, J. Chem. Theory Comput. 113 (2017), 5966.
[6] K. Boguslawski, J. Chem. Phys. 145 (2017), 234105.
[7] K. Boguslawski, J. Chem. Phys. 147 (2017), 139901.
[8] K. Boguslawski, J. Chem. Theory Comput. (2018), doi: 10.1021/acs.jctc.8b01053.