Efficient Implementation of the Spin-Free Renormalized Internally-Contracted Multireference Coupled Cluster Theory
Kalman Szenes, Riya Kayal, Kantharuban Sivalingam, Robin Feldmann, Frank Neese, Markus Reiher
TL;DR
This paper presents an efficient implementation of a multireference coupled cluster method in the ORCA program, enabling accurate quantum chemistry calculations on large systems.
Contribution
An efficient, parallelized implementation of RIC-MRCCSD using a spin-free formulation and code generation tools.
Findings
The RIC-MRCCSD implementation achieves substantial efficiency gains and runs in parallel with speedups on multiple cores.
The method scales well to large systems, demonstrated by computing the ground state of a vitamin B12 model with a CAS(12,12) active space.
RIC-MRCCSD is more efficient than alternative methods like IC-MRCCSD, which require higher-order density matrices.
Abstract
In this paper, an efficient implementation of the renormalized internally contracted multireference coupled cluster with singles and doubles (RIC-MRCCSD) into the ORCA quantum chemistry program suite is reported. To this end, Evangelista’s Wick&d equation generator was combined with ORCA’s native AGE code generator in order to implement the many-body residuals required for the RIC-MRCCSD method. Substantial efficiency gains are realized by deriving a spin-free formulation instead of the previously reported spin–orbital version developed by some of us. Since AGE produces parallelized code, the resulting implementation can directly be run in parallel with substantial speedups when executed on multiple cores. In terms of runtime, the cost of RIC-MRCCSD is shown to be between single-reference RHF-CCSD and UHF-CCSD, even when active space spaces as large as CAS(14,14) are considered. This…
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Taxonomy
TopicsAdvanced Chemical Physics Studies · Spectroscopy and Quantum Chemical Studies · Magnetism in coordination complexes