Configuration interaction singles

The simplest and most widely-employed method is the so-called configuration interaction singles or CIS method. This involves singleelectron promotions only (from occupied molecular orbitals in the reference wavefunction to unoccupied molecular orbitals). Because there are relatively few of these, CIS is in fact practical for molecules of moderate complexity. As noted previously, single-electron promotions do not lead to improvement in either the ground-state wavefunction or energy over the corresponding Hartree-Fock... 

A number of methods have been proposed for calculations of the geometries of molecules in excited states. These include CIS (Configuration Interaction Singles) and variations on CIS to account for the effect of double substitutions, as well as so-called time dependent density functional models. Except for CIS (the simplest of the methods) there is very little practical experience. There is also very little solid experimental data on the geometries of excited-state molecules. 

CIS Model. Configuration Interactions Singles. A limited Configuration Interaction scheme in which only single excitations from occupied to unoccupied molecular orbitals are considered. This is perhaps the simplest method available to the description of Excited States of molecules. 

Let s compare these CASSCF results with those for a method that is not size-consistent, Cl with no complete aspect. We ll use CISD (configuration interaction singles and doubles Section 5.4.3). Here are the results for CISD/6-31G ... 

Pending ongoing developments of improved functionals, an effective multi-scale scheme (sketched in Figure 2.3) can be profitably used, where the NO moiety is treated at the Quadratic Configuration Interaction Single and Double (QCISD) level of theory and the remaining parts of the system are treated by means of hybrid density functionals ... 

H.-C. Chen and C.-P. Hsu, Ab initio characterization of electron transfer coupling in photoin-duced systems generalized Mulliken-Hush with configuration-interaction singles, J. Phys. Chem. A, 109 (2005) 11989-11995. 

There are several single reference methods to compute electronic transition energies. Among them are configuration interaction-singles (CIS) [48], random-phase approximation (RPA) [49, 50], equation-of-motion couple cluster (EOMCC)... 

Keywords Configuration-Interaction Singles, Time-Dependent Density-Functional Theory,... 

Coupled-cluster singles and doubles Configuration-interaction Configuration-interaction singles... 

Configuration-interaction singles with a second-order Mpller-Plesset correction... 

Configuration-interaction singles with a doubles correction Configuration-interaction singles with a third-order... 

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