Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States

Abstract

The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments.

Accurate Excited-State Geometries: A CASPT2 and Coupled-Cluster Reference Database for Small Molecules

“…80 On the theoretical side, one can find a very complete CASPT2/6-31+G(d) investigation of the Morokuma group devoted to the dissociation paths of ketene, 81 as well as an earlier investigation of Szalay and co-workers with CC methods for the same molecule. 82 The structure of the lowest ES structure of diazomethane, constrained in the C 2 v symmetry, was previously determined at both CASPT2/6-31G(d) 26 and CC2/TZVP 25 levels of theory, whereas a CASSCF/6-31G(d) investigation of the ES pathways relating diazirine to diazomethane has also been performed. 83 …”

“…30–50 atoms) and do not involve the choice of an XCF. However, these methods were reported to overestimate some bond lengths especially for the keto group, 6,22,25,28,41 and caution is necessary before using them as references.…”

The dimer-approach to characterize opto-electronic properties of and exciton trapping and diffusion in organic semiconductor aggregates and crystals

“…However, it has to be coupled with an appropriate density functional or wave function based approach because it is not able to provide reliable information about the ground state energy surface. It is interesting to note that more sophisticated semi-empirical methods as the OMx-approaches of Thiel and coworkers 91,92 seem to be less suitable. 85 More information about these studies can be found in Section 3.6.…”

A QTAIM and stress tensor investigation of the torsion path of a light-driven fluorene molecular rotary motor

“…Fulfillment of this task is impossible without comprehensive understanding of the factors underlying the mechanism of action of these devices. In this regard, the methods of analyzing the total electronic density distributions ρ ( r ), such as the quantum theory of atoms in molecules QTAIM and stress tensor analysis methods, can provide complimentary information to the well established approaches analyzing the shape of the potential energy surfaces (PESs) of the ground and excited electronic states of the target compounds . Recently, some of us have developed QTAIM/stress tensor theory for use on the photoisomerization of the retinal chromophore and explored the implications of preferred direction of torsion − φ or + φ of the chromophore upon the photoexcitation …”

“…In this regard, the methods of analyzing the total electronic density distributions q(r), such as the quantum theory of atoms in molecules QTAIM [11] and stress tensor analysis methods, can provide complimentary information to the well established approaches analyzing the shape of the potential energy surfaces (PESs) of the ground and excited electronic states of the target compounds. [12][13][14][15][16][17][18] Recently, some of us have developed QTAIM/stress tensor theory for use on the photoisomerization of the retinal chromophore and explored the implications of preferred direction of torsion 2u or 1u of the chromophore upon the photoexcitation. [19] In this work, we will apply the QTAIM/stress tensor analysis to a different photodriven system, the 9-[(2R)22,4,7-trimethyl-1indanylidene]fluorene light-driven molecular rotary motor (1).…”