Coupled Cluster Method with Single and Double Excitations Tailored by Matrix Product State Wave Functions

The origins of the coupled cluster method are described. Special attention is paid to the arguments put forward for the exponential structure of the wave functions. Various approximation schemes invented during the last 40 years are presented. The problems arising from these approximations necessarily truncating or destroying the exponential form are discussed and ways to deal with them are described.

Download Full-text

Equation-of-Motion Coupled-Cluster Method with Double Electron-Attaching Operators: Theory, Implementation, and Benchmarks

10.26434/chemrxiv.13379948.v2 ◽

2020 ◽

Author(s):

Sahil Gulania ◽

Eirik Fadum Kjønstad ◽

John F. Stanton ◽

Henrik Koch ◽

Anna Krylov

Keyword(s):

Particle Density ◽

Equation Of Motion ◽

Wave Functions ◽

Cluster Method ◽

Coupled Cluster ◽

Bond Breaking ◽

Coupled Cluster Method ◽

Density Matrices ◽

Double Electron ◽

Structure Patterns

<div> <div> <div> <p>We report a production-level implementation of equation-of-motion coupled-cluster method with double electron- attaching EOM operators of 2p and 3p1h types, EOM-DEA-CCSD. This ansatz, suitable for treating electronic structure patterns that can be described as two-electrons-in-many orbitals, represents a useful addition to EOM-CC family of methods. We analyze the performance of EOM-DEA-CCSD for energy differences and molecular properties. By considering reduced quantities, such as state and transition one-particle density matrices, we can compare EOM-DEA- CCSD wave-functions with wave-functions computed by other EOM-CCSD methods. The benchmarks illustrate that EOM-DEA-CCSD capable of treating diradicals, bond-breaking, and some types of conical intersection. </p> </div> </div> </div>

Download Full-text

EOM-CC Guide for Fock-Space Travel: The C2 Edition

10.26434/chemrxiv.7368299 ◽

2018 ◽

Author(s):

Sahil Gulania ◽

Thomas-C. Jagau ◽

Anna I. Krylov

Keyword(s):

Electronic Structure ◽

Ionization Potential ◽

Fock Space ◽

Wave Functions ◽

Cluster Method ◽

Coupled Cluster ◽

Space Travel ◽

Electron Detachment ◽

Coupled Cluster Method ◽

Structure Calculations

Despite their small size, C<sub>2</sub> species pose a big challenge to electronic structure owing to extensive electronic degeneracies and multi-configurational wave functions leading to a dense manifold of electronic states. We present detailed electronic structure calculations of C<sub>2</sub>, C<sub>2</sub><sup>-</sup>, and C<sub>2</sub><sup>2-</sup> emphasizing spectroscopically relevant properties. We employ double ionization potential (DIP) and ionization potential (IP) variants of equation-of-motion coupled-cluster method with single and double substitutions (EOM-CCSD) and a dianionic reference state. We show that EOM-CCSD is capable of describing multiple interacting states in C<sub>2</sub> and C<sub>2</sub><sup>-</sup> in an accurate, robust, and effective way. We also characterize the electronic structure of C<sub>2</sub><sup>2-</sup>, which is metastable with respect to electron detachment.

Download Full-text