Benchmarking the performance of spin-component scaled CC2 in ground and electronically excited states

Articles you may be interested inInfluences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy J. Chem. Phys. 143, 034308 (2015); 10.1063/1.4927004The weak hydrogen bond in the fluorobenzene-ammonia van der Waals complex: Insights into the effects of electron withdrawing substituents on π versus in-plane bonding J. Chem. Phys. 126, 154319 (2007) The 1-naphthol·cyclopropane intermolecular complex is formed in a supersonic jet and investigated by resonant two-photon ionization (R2PI) spectroscopy, UV holeburning, and stimulated emission pumping (SEP)-R2PI spectroscopy. Two very different structure types are inferred from the vibronic spectra and calculations. In the "edge" isomer, the OH group of 1-naphthol is directed towards a C-C bond of cyclopropane, the two ring planes are perpendicular. In the "face" isomer, the cyclopropane is adsorbed on one of the π-aromatic faces of the 1-naphthol moiety, the ring planes are nearly parallel. Accurate ground-state intermolecular dissociation energies D 0 were measured with the SEP-R2PI technique. The D 0 (S 0 ) of the edge isomer is bracketed as 15.35 ± 0.03 kJ/mol, while that of the face isomer is 16.96 ± 0.12 kJ/mol. The corresponding excited-state dissociation energies D 0 (S 1 ) were evaluated using the respective electronic spectral shifts. Despite the D 0 (S 0 ) difference of 1.6 kJ/mol, both isomers are observed in the jet in similar concentrations, so they must be separated by substantial potential energy barriers. Intermolecular binding energies, D e , and dissociation energies, D 0 , calculated with correlated wave function methods and two dispersion-corrected density-functional methods are evaluated in the context of these results. The density functional calculations suggest that the face isomer is bound solely by dispersion interactions. Binding of the edge isomer is also dominated by dispersion, which makes up two thirds of the total binding energy. Published by AIP Publishing. [http://dx

Section: Theoretical Methodsmentioning

confidence: 99%

Accurate dissociation energies of two isomers of the 1-naphthol⋅cyclopropane complex

Maity

Knochenmuss

Holzer

et al. 2016

“…This scaling enhances the accuracy of 0-0 transition energies both for ππ * and nπ * states. 42 In a recent benchmark study, it was shown that the standard deviation of 0-0 transition energies for a set of organic molecules is 0.06 eV. 43 For the calculations of SCS-CC2 energies we used the standard scaling factors 1/3 for the same-spin and 6/5 for the opposite-spin components.…”

Section: A Computational Methodsmentioning

confidence: 99%

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Lobsiger

Etinski

Blaser

et al. 2015

Intersystem crossing rates of S 1 state keto-amino cytosine at low excess energy The amino-keto tautomer of supersonic jet-cooled cytosine undergoes intersystem crossing (ISC) from the v = 0 and low-lying vibronic levels of its S 1 ( 1 ππ * ) state. We investigate these ISC rates experimentally and theoretically as a function of S 1 state vibrational excess energy E exc . The S 1 vibronic levels are pumped with a ∼5 ns UV laser, the S 1 and triplet state ion signals are separated by prompt or delayed ionization with a second UV laser pulse. After correcting the raw ISC yields for the relative S 1 and T 1 ionization cross sections, we obtain energy dependent ISC quantum yields Q corr ISC = 1%-5%. These are combined with previously measured vibronic state-specific decay rates, giving ISC rates k ISC = 0.4-1.5 · 10 9 s −1 , the corresponding S 1 S 0 internal conversion (IC) rates are 30-100 times larger. Theoretical ISC rates are computed using SCS-CC2 methods, which predict rapid ISC from the S 1 ; v = 0 state with k ISC = 3 · 10 9 s −1 to the T 1 ( 3 ππ * ) triplet state. The surprisingly high rate of this El Sayed-forbidden transition is caused by a substantial admixture of 1 n O π * character into the S 1 ( 1 ππ * ) wave function at its non-planar minimum geometry. The combination of experiment and theory implies that (1) below E exc = 550 cm −1 in the S 1 state, S 1 S 0 internal conversion dominates the nonradiative decay with k IC ≥ 2 · 10 10 s −1 , (2) the calculated S 1 T 1 ( 1 ππ * 3 ππ * ) ISC rate is in good agreement with experiment, (3) being El-Sayed forbidden, the S 1 T 1 ISC is moderately fast (k ISC = 3 · 10 9 s −1 ), and not ultrafast, as claimed by other calculations, and (4) at E exc ∼ 550 cm −1 the IC rate increases by ∼50 times, probably by accessing the lowest conical intersection (the C5-twist CI) and thereby effectively switching off the ISC decay channels. C 2015 AIP Publishing LLC. [http://dx

“…Accurate electron-correlation methods, such as high-order configuration interaction (CI) or coupledcluster (CC) schemes, yield excitation energies in close agreement with experiment when using large basis sets. [1][2][3][4][5] However, high-order CI and CC calculations are limited to very small molecules, 6 often comprising no more than a few tens of atoms, and therefore not applicable for studying a) Electronic mail: Robert.Send@kit.edu. b) Electronic mail: Ville.Kaila@nih.gov.…”

Section: Introductionmentioning

confidence: 99%

Reduction of the virtual space for coupled-cluster excitation energies of large molecules and embedded systems

Send¹,

Kaila²,

Sundholm³

2011

We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50 eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1 eV. By using a RVS energy threshold of 50 eV, the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2/TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics/molecular mechanics separation schemes.