Complete active space self-consistent field CASSCF/CASPT2 calculations

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). 

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. 

Basis Sets Correlation Consistent Sets Circular Dichro-ism Electronic Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Density Functional Applications Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Electronic Diabatic States Definition, Computation, and Applications ESR Hyperfine Calculations Magnetic Circular Dichroism of rt Systems Non-adiabatic Derivative Couplings Relativistic Theory and Applications Structure Determination by Computer-based Spectrum Interpretation Valence Bond Curve Crossing Models. 

Both density functional theory (DPT) and multiconfigura-tional perturbation theory, that is, complete active space self-consistent field (CASSCF) followed by second-order perturbation theory (CASPT2), were used to investigate the heterolytic and homolytic dissociation enthalpies of RuCp2 and RuCpPy. The enthalpies of nine possible reaction steps involved in the dissociation (R1-R9, see Figs. 2, 3) were computed. All DFT calculations were performed with Turbomole v. 6.3 [9], while the CASSCF/CASPT2 calculations were performed with Molcas 7.6 [10]. 

More recently, Arenas and co-workers studied the diazirine system at the complete active space, self-consistent field (CASSCF) level of theory using the cc-pVDZ basis set to map the potential energy surfaces with the critical points recalculated at the CASPT2/cc-pVDZ level.The active space used for these calculations was 12 electrons in 10 orbitals. Additionally, they performed limited direct dynamic trajectory calculations on the S, and Sj surfaces. The key features of the potential energy surfaces are depicted in Figure 92.2. 

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