A fully quantum mechanical simulation study on the lowest n-π∗ state of hydrated formaldehyde

Histograms of n-π∗ excitation energies (in eV) of the hydrated formaldehyde, where total of 400 samples were calculated by the method of configuration interaction singles with perturbative doubles correction, CIS(D), in conjunction with the multilayer version of fragment molecular orbital (MLFMO) scheme. These samples were generated by molecular dynamics (MD) simulation on a droplet cluster consisting of a formaldehyde molecule and 128 water molecules. During the MD run, the total energy and gradient were calculated 'on-the-fly' at the FMO-based Hartree-Fock/6-31G level. A series of MLFMO-CIS(D)/6-31G∗ calculations were then performed with a setting that six nearest water molecules are included in the chromophore region with the formaldehyde molecule (denoted as FRM+6W/122W). The averaged value of CIS and CIS(D) energies over 400 samples were 4.96 eV and 4.22 eV, respectively.