Calculations of n→π* Transition Energies: Comparisons Between TD-DFT, ADC, CC, CASPT2, and BSE/GW Descriptions

Abstract

Using a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), CASPT2, time-dependent density functional theory (TD-DFT), and BSE/evGW, the two latter combined with different exchange-correlation functionals, we investigate the lowest singlet transition in 23 n→π* compounds based on the nitroso, thiocarbonyl, carbonyl, and diazo chromophores. First, for 16 small derivatives we compare the transition energies provided by the different wave function approaches to define theoretical best estimates. For this set, it surprisingly turned out that ADC(2) offers a better match with CC3 than ADC(3). Next, we use 10 functionals belonging to the "LYP" and "M06" families and compare the TD-DFT and the BSE/evGW descriptions. The BSE/evGW results are less sensitive than their TD-DFT counterparts to the selected functional, especially in the M06 series. Nevertheless, BSE/evGW delivers larger errors than TD-CAM-B3LYP, which provides extremely accurate results in the present case, especially when the Tamm-Dancoff approximation is applied. In addition, we show that, among the different starting points for BSE/evGW calculations, M06-2X eigenstates stand as the most appropriate. Finally, we confirm that the trends observed on the small compounds pertain in larger molecules.

A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Medium Size Molecules

“…Let us now turn our attention to the excited states of three pseudo-linear -conjugated systems that have been the subject to several investigations in the past, namely, acrolein, 27,[117][118][119][127][128][129][130][131] butadiene, 23,26,27,71,118,128,[132][133][134][135][136][137][138][139][140][141][142][143] and glyoxal. 27,114,118,128,130,[144][145][146][147] Among these works, it is worth highlighting the detailed theoretical investigation of Saha, Ehara, and Nakatsuji, who reported a huge number of ES for these three systems using a coherent theoretical protocol based on the symmetry-adapted-cluster configuration interaction (SAC-CI) method. 128 In the following, these three molecules are considered in their most stable trans conformation.…”

A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Medium Size Molecules

“…Let us now turn our attention to the excited states of three pseudo-linear π-conjugated systems that have been the subject to several investigations in the past, namely, acrolein, 27,[119][120][121][129][130][131][132][133] butadiene, 23,26,27,72,120,130,[134][135][136][137][138][139][140][141][142][143][144][145] and glyoxal. 27,116,120,130,132,[146][147][148][149] Among these works, it is worth highlighting the detailed theoretical investigation of Saha, Ehara, and Nakatsuji, who reported a huge number of ES for these three systems using a coherent theoretical protocol based on the symmetry-adapted-cluster configuration interaction (SAC-CI) method. 130 In the following, these three molecules are considered in their most stable trans conformation.…”

Is ADC(3) as Accurate as CC3 for Valence and Rydberg Transition Energies?

“…ADC(3) was subsequently employed to perform theory vs experiment comparisons, [17][18][19][20][21][22][23] and to define benchmark values for assessing lower-order methods. [24][25][26][27] Given, on the one hand, that ADC(3) was advocated as a benchmark method and, on the other hand, the recent availability of high-accuracy reference energies for a large panel of ES, 15,28,29 we believe that the time has come to perform a new performance assessment of this method. To this end, we have first considered our most recent set of TBE/augcc-pVTZ obtained for vertical transition energies in organic compounds encompassing from one to six non-hydrogen atoms.…”