A Mountaineering Strategy to Excited States: Highly Accurate Reference Energies and Benchmarks

• DOI: 10.1021/acs.jctc.8b00406
• Publication Date: 2018-07-02T22:35:43Z
• Authors: Pierre-François Loos; Anthony Scemama; Aymeric Blondel; Yann Garniron; Michel Caffarel; Denis Jacquemin
• Keywords: Transition state; Acetylene; Coupled cluster

Striving to define very accurate vertical transition energies, we perform both high-level coupled cluster (CC) calculations (up CCSDTQP) and selected configuration interaction (sCI) several millions of determinants) for 18 small compounds (water, hydrogen sulfide, ammonia, chloride, dinitrogen, carbon monoxide, acetylene, ethylene, formaldehyde, methanimine, thioformaldehyde, acetaldehyde, cyclopropene, diazomethane, formamide, ketene, nitrosomethane, the smallest streptocyanine). By systematically increasing order CC expansion, number determinants in CI expansion as well size one-electron basis set, have been able reach near full (FCI) quality energies. These are carried out on CC3/aug-cc-pVTZ geometries, using a series increasingly large atomic sets including diffuse functions. In this way, list 110 energies states various characters (valence, Rydberg, n → π*, π singlet, triplet, etc.) be used references further calculations. Benchmark provided at aug-cc-pVTZ level with additional set corrections, obtain results close complete limit. reference data benchmark 12 excited-state wave function methods accounting double triple contributions, namely ADC(2), ADC(3), CIS(D), CIS(D∞), CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, CC3, CCSDT., CCSDTQ. It turns that CCSDTQ yields negligible difference extrapolated values mean absolute error 0.01 eV, whereas approaches iterative triples also (mean 0.03 eV). Consequently, CCSDT-3 CC3 can reliable benchmarks. This observation does not hold ADC(3) delivers quite errors compounds, clear tendency overcorrect its second-order version, ADC(2). Finally, discuss possibility use extrapolation so tackle more easily larger compounds.