AN ABINITIO STUDY OF THE POTENTIAL-ENERGY SURFACE FOR THE O-H---O BOND IN KH2PO4

A methodology is presented for carrying out ab-initio molecular orbital calculation of the potential energy surface as a function of position of the H atom in the O-H---O bonds of KH2PO4 (KDP). The calculations employ the Hartree-Fock Self-Consistent-Field (SCF) approach utilizing the Linear Combination of Atomic Orbital for Molecular Orbital (LCAOMO) procedure with basis in Gaussian form. This approach seems to yield a reliable representation of double-minimum potential well for the O-H---O bond in KDP, as judged from the agreement between the predicted (0.3604 angstrom) and experimental (0.3674 angstrom) values for the separation between the two equilibrium positions of the H atom along the O---O direction. The calculated value of the barrier height (0.08 eV) helps clarify some earlier spectroscopic data on the activation energy for the motion of the H-atom in the O-H---O bond in KDP. The same methodology should be applicable for investigating the possible double-minimum wells for the heavier atoms in the KDP-type of ferroelectrics and antiferroelectrics.