Multideterminant Methods

In multireference CISD (MRCISD) calculations, the wavefunction is written as 

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In this context one should also mention the rather old MRD-CI-method of Buenker and Peyerimhoff [160]. There one starts from a multideterminant reference function and improves it by Cl with single and double substitution. This method has not been designed for single states, but rather for the computation of various states simultaneously. 

Multideterminations of species are of great interest to kinetic methods of analysis. Various mathematical algorithms allow exploiting of the whole kinetic curve to determine the concentrations of two or more analytes in a mixture. 

Electron structure calculations often become difficult when transition metals are involved. If the system has incomplete d shells many electron configurations contribute even to the ground state leading to non-dynamical electron correlation. Wave function-based methods with multideterminant references are required for high accuracy. Density functional theory is often successful, but no current functional is reliable for transition metals compounds in general. QMC as a wave function-based method has to use multideterminant... 

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