Gaussian program DENSITY=CURRENT

In the Gaussian series of programs, the properties of the correlated wavefunction are obtained only if the density=current keyword is supplied. 

The root=l parameter of the CIS keyword specifies the excited state i = 1 (consistent with the notation in Sidebar 11.1), and density=current requests that density corrections for this excited state (rather than the default ground state) he stared for subsequent NBO analysis ( pop=nboread ). The fixdm keyword in the nbokeylist applies an additional correction to prevent unphysical (negative or Pauli-violating) orbital populations from the CIS-corrected density as approximated by the Gaussian program. 

Time resolved laser spectroscopy is likely the best method to get kinetic information on transient states. More information can currently be gained from quantum mechanical calculations at relatively high level of theory using the Gaussian Suite of programs (ab initio and density functional theory). 

Basically, density functional theory (DFT) is similar to the ab initio method, but it is not based on a wavefunction. Instead, the energy is computed as a functional of the electron density (16). The DFT methods were developed that are much faster than Gaussian-style programs. Currently, many functional approximations are in use. 

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