MRDCI method

The wavefunction, which is used in such an MRDCI approach to compute molecular properties other than energy, includes the zeroth-order reference list plus all selected configurations (generally between 20000 and 100000), The disadvantage of this MRDCI method is that it cannot be handled as a black box program, and that the contribution of the unselected species may become quite large (and different... 

The spin projection methods discussed so far apply the projection after the wavefunction has been determined. A second approach is to construct the wavefunction so that there is no spin contamination from the beginning. This leads to methods such as ROHF and restricted open-shell M0ller-Plesset perturbation theory (ROMPn)," and to valence bond, MCSCF, and Cl and MRDCI methods that use spin-adapted configurations. 

Another class of methods uses more than one Slater determinant as the reference wave function. The methods used to describe electron correlation within these calculations are similar in some ways to the methods listed above. These methods include multiconfigurational self-consistent field (MCSCF), multireference single and double configuration interaction (MRDCI), and /V-clcctron valence state perturbation theory (NEVPT) methods.5... 

In order to discuss the ability of the MRDCI/BK method to predict the isotropic hfcc s and to study the reasons responsible for the poor agreement found in the configuration selected MR-CI calculation in the CCF [10] and CXF [55] studies, an investigation was performed at the geometry used in both these previous works. The AO basis sets used are given in table 10. The... 

The prototypical Na- - -HF system has been investigated by the same method. It represents an excellent example where elaborate and accurate calculations (MRDCI)[75] are possible for the ground and excited states of the complex. Also,... 

Reasonable correlation between measured and calculated TPA was observed for a series of chromophores with medium size [123, 131, 132, 224, 227, 233, 284, 285, 289, 295-300]. However, problems can arise for larger molecules requiring larger Cl space. Under these circumstances, the calculated quantities A/(0. M(y, M02, oi, and 02 may not reliably describe TPA according to Eq. (18). Despite these problems, semiempirical calculations of Im[ (— o. co)] have been the most applied method for a theoretical design of chromophores with large TP absorptivity [131, 132, 233, 283-285, 287-289, 301]. Hence, ZINDO/S-MRDCI has become an attractive theoretical tool for the calculation of TPA due to the modest calculation time. 

INDO-MRDCI/SOS method. This example demonstrates the tuning effect on <5 by the number of dipolar arms. This is larger in 108a in comparison with 108b. 

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