Analytic Gradients of Approximate Coupled Cluster Methods with Quadruple Excitations

The analytic gradient theory for both iterative and noniterative coupled-cluster approximations that include connected quadruple excitations is presented. These methods include, in particular, CCSDT(Q), which is an analog of the well-known CCSD(T) method which starts from the full CCSDT method rather than CCSD. The resulting methods are implemented in the CFOUR program suite, and pilot applications are presented for the equilibrium geometries and harmonic vibrational frequencies of the simplest Criegee intermediate, CH2OO, as well as to the isomerization pathway between dimethylcarbene and propene. While all methods are seen to approximate the full CCSDTQ results well for "well-behaved" systems, the more difficult case of the Criegee intermediate shows that CCSDT(Q), as well as certain iterative approximations, display problematic behavior.

Medienart:

E-Artikel

Erscheinungsjahr:

2020

Erschienen:

2020

Enthalten in:

Zur Gesamtaufnahme - volume:16

Enthalten in:

Journal of chemical theory and computation - 16(2020), 10 vom: 13. Okt., Seite 6195-6206

Sprache:

Englisch

Beteiligte Personen:

Matthews, Devin A [VerfasserIn]

Links:

Volltext

Themen:

Journal Article

Anmerkungen:

Date Revised 13.10.2020

published: Print-Electronic

Citation Status PubMed-not-MEDLINE

doi:

10.1021/acs.jctc.0c00522

funding:

Förderinstitution / Projekttitel:

PPN (Katalog-ID):

NLM313616329