Complete active space perturbation theory CASPT2 calculations

The results are summarized in Tables 20.3 and 20.4. The calculations with CAS-SCF and CAS-QDPT are far too large to be done. We, therefore, compare the results with available experimental results and some recent theoretical results, i.e. MR-Cl results by Hachey et al. [39], the second-order complete active space perturbation theory (CASPT2) calculations by Merchan and Roos [40], and the equation of motion coupled cluster (EOM-CC) calculations by Gwaltney and Bartlett [41]. 

Our results for the vertical excitation energies (VEEs) of the four lowest-lying singlet excited electronic states are presented in Tables. 1, in comparison with previous calculations and experimental data. Previous calculations include the complete active space second-order perturbation theory (CASPT2) calculations of... 

Reaction field theory with a spherical cavity, as proposed by Karlstrom [77, 78], has been applied to the calculation of the ECD spectrum of a rigid cyclic diamide, diazabicyclo[2,2,2]octane-3,6-dione, in an aqueous environment [79], In this case, the complete active space self-consistent field (CASSCF) and multiconfigurational second-order perturbation theory (CASPT2) methods were used. The qualitative shape of the solution-phase spectrum was reproduced by these reaction field calculations, although this was also approximately achieved by calculations on an isolated molecule. 

In order to correlate the solid state and solution phase structures, molecular modelling using the exciton matrix method was used to predict the CD spectrum of 1 from its crystal structure and was compared to the CD spectrum obtained in CHC13 solutions [23]. The matrix parameters for NDI were created using the Franck-Condon data derived from complete-active space self-consistent fields (CASSCF) calculations, combined with multi-configurational second-order perturbation theory (CASPT2). 

We continue this section by pointing out that calculations exist that combine (PT) and MC methods. For example, methods such as complete active space, second order perturbation theory (CASPT2) and multi-configuration quasidegenerate perturbation theory MCODPT use a MC wave function as the reference. PT, generally to second order, is used to estimate the contribution from excited states that arise from excitation outside the original active space of the MC calculation. 

Most of the description of metal-metal multiple bonds presented in this paper are based on calculations performed with the complete active space self-consistent-fleld (CASSCF) method [8] followed by second order perturbation theory, CASPT2 [9], The CASSCF method guarantees a qualitatively correct representation of the electronic structure, and the metal-metal multiple bonds. The subsequent... 

Theoretical calculations were performed, initially with SCF-Xa-SW methods on a truncated model [16], and later with the complete active space self-consistent field (CASSCF) and mul-ticonfigurational complete active space second-order perturbation theory (CASPT2) methods on the full molecule [15]. The electronic structures from the two calculations were remarkably similar. The CASSCF/PT2 calculations predicted a single, dominant configuration (73%) with (a) (x) (x ) (a ) (8) (5 ). Although the formal bond order is 1.5, the effective bond order, which considers minor configurations that contribute to the ground-state wavefunction, is lower at 1.15. 

As an illustration of the performance of TDDFT, we compare various density functionals and wave function methods for the first singlet excited states of naphthalene in Tables 4, 5, and 6. All calculations were performed using the aug-TZVP basis set, while the complete active space self-consistent field (SCF) with second-order perturbation theory (CASPT2) results from Ref. 200 were obtained in a smaller double-zeta valence basis set with some diffuse augmentation. The experimental results correspond to band maxima from gas-phase experiments however, the position of the band maximum does not necessarily coincide with the vertical excitation energy, especially if... 

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