QUESTDB: A database of highly accurate excitation energies for the electronic structure community

Abstract

We describe our efforts of the past few years to create a large set of more than 500 highly accurate vertical excitation energies of various natures (π → π*, n → π*, double excitation, Rydberg, singlet, doublet, triplet, etc.) in small‐ and medium‐sized molecules. These values have been obtained using an incremental strategy which consists in combining high‐order coupled cluster and selected configuration interaction calculations using increasingly large diffuse basis sets in order to reach high accuracy. One of the key aspects of the so‐called QUEST database of vertical excitations is that it does not rely on any experimental values, avoiding potential biases inherently linked to experiments and facilitating theoretical cross comparisons. Following this composite protocol, we have been able to produce theoretical best estimates (TBEs) with the aug‐cc‐pVTZ basis set for each of these transitions, as well as basis set corrected TBEs (i.e., near the complete basis set limit) for some of them. The TBEs/aug‐cc‐pVTZ have been employed to benchmark a large number of (lower‐order) wave function methods such as CIS(D), ADC(2), CC2, STEOM‐CCSD, CCSD, CCSDR(3), CCSDT‐3, ADC(3), CC3, NEVPT2, and so on (including spin‐scaled variants). In order to gather the huge amount of data produced during the QUEST project, we have created a website (https://lcpq.github.io/QUESTDB_website) where one can easily test and compare the accuracy of a given method with respect to various variables such as the molecule size or its family, the nature of the excited states, the type of basis set, and so on. We hope that the present review will provide a useful summary of our effort so far and foster new developments around excited‐state methods. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods

How accurate are EOM-CC4 vertical excitation energies?

“…Recently, a large collection of deterministic, stochastic or hybrid selected CI (SCI) methods [40][41][42] has (re)appeared [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] in the electronic structure landscape providing an alternative route to highly-accurate ground-and excited-state energies [58][59][60][61][62][63][64][65][66][67][68][69][70] (see Refs. 71 and 72 for recent reviews).…”

“…42,67,73,74 By iteratively increasing the number of determinants of the variational space and supplementing it with a second-order perturbative correction (PT2), the SCI+PT2 family of methods has been recently shown to produce near-FCI correlation and excitation energies for small-and medium-size molecules in compact basis sets. 58,[61][62][63][64][65]67,70 Although the formal scaling of such algorithms remain exponential, the prefactor is greatly reduced which explains their current attractiveness in the electronic structure community and much wider applicability than their standard FCI parent.…”

“…Taking advantage of the high accuracy of CC and SCI+PT2 methods, we have very recently created a large dataset gathering more than 500 highly-accurate vertical excitation energies for electronic transitions of various natures (valence, Rydberg, n → π * , π → π * , singlet, doublet, triplet, chargetransfer, and double excitations) in small-and medium-sized molecules ranging from diatomics to molecules as large as naphthalene. 61,[63][64][65]70,71 The main purpose of this so-called QUEST database is to provide reference excitation energies in order to perform fair and reliable benchmarks between electronic structure methods and assess their strengths and weakness for a large panel of chemical scenarios. Most of these reference transition energies, which rely exclusively on highlevel ab initio calculations, can be reasonably considered as chemically accurate, i.e., within 1 kcal mol −1 or 0.043 eV of the FCI limit.…”

High-throughput virtual screening for organic electronics: a comparative study of alternative strategies

“…If computed data for excited state properties are to be considered for calibration, there are very high-level reference datasets available. [212][213][214][215][216][217] For example, the excited states, including triplets, of 18 small molecules, e.g. water, acetylene etc.…”

Excited States of Xanthophylls Revisited: Toward the Simulation of Biologically Relevant Systems

“…In particular, we note a good agreement between the two for the dark B u – state, but also for the dark A g state, both being characterized by significant contributions from double excitations. At this stage, we recall that CC3 was shown to slightly overestimate the excitation energies of the dark A g state of butadiene and hexatriene, but to be rather competitive with multireference methods, 11 for these short systems in which the contributions of the doubles in the A g state remain limited to ca. 25%.…”