PRELIMINARY DENSITY-FUNCTIONAL CALCULATIONS ON THE FORMIC-ACID DIMER

The utility of density functional theory (DFT) to simulate the energet ics of intermolecular rearrangement, dissociation energy, and, as well as the fine topological features of the molecular charge distribution has been tested for the formic acid dimer. The equilibrium and transi tion state structures are optimized using adiabatic connection method (ACM) and the barriers to the double proton transfer reaction have bee n also evaluated. The ACM results are compared with those obtained fro m SCF, MP2 and various DFT functionals. Preliminary results indicate t hat there is perhaps a significant role of the correlation effects in determining the barrier height for this reaction. The formic acid dime r dissociation energies calculated from the non-local gradient correct ed or ACM functionals are in reasonable agreement with experimental es timates. Comparison of the DFT, SCF and MP2 electrostatic molecular po tentials derived from cumulative atomic multipole moments (CAMM) for t he formic acid dimer indicates that the correlation effects are reprod uced correctly, providing that DFT atomic charges are supplemented by higher atomic multipole moments.