Akademik Veri Yönetim Sistemi
17TH INTERNATIONAL CONGRESS OF QUANTUM CHEMISTRY, Bratislava, Slovakya, 26 Haziran - 01 Temmuz 2023, ss.1
Coupled-cluster theory (CC) provides a systematic access to highly accurate solutions of the
electronic Schrödinger equation. The investigation of systems with chellenging open-shell electronic structures requires an extension to multiconfigurational references. Internally contracted
multireference coupled-cluster theory (icMRCC) has been developed as such an extension, with
the aim of maximum analogy and compatibility to standard coupled-cluster theory. In this
contribution, we analyze the accuracy of the icMRCCSD(T) method [1] in comparison to the
standard CC hierarchy. The use of large basis sets appears important for drawing the correct
conclusions. We will in particular discuss the choice of the zeroth-order Hamiltonian and the
impact of pragmatic approximations introduced in Ref. [1].
Another aspect in comparison to standard CC theory is the increased computational effort of
icMRCC approaches [2]. One option to reduce the computation time is a hybrid approach, which
replaces computationally expensive, but for the overall accuracy less relevant terms by simpler
expressions inspired by multireference coupled-electron pair approximations (MRCEPA). We
have recently investigated the use of MRCEPA(0), here we explore alternative formulations
using further MRCEPA variants.[3]