MULTI-COMPONENT FIRST-PRINCIPLES CALCULATION ON ISOTOPE EFFECT IN HYDROGEN-BONDED DIELECTRIC MATERIALS K3H(SO4)2 AND K3D(SO4)2

We have theoretically elucidated the origin of the isotope effect on phase transition temperature in hydrogen-bonded ferroelectric materials K3H(SO4)2 and K3D(SO4)2, using the cluster models with multi-component molecular orbital (MC_MO) method, which can determine both electronic and nuclear wave functions simultaneously. We have confirmed that the origin of the isotope effect is the localization of the nuclear wave function by deuterization. We have also demonstrated the isotope effect in potential energies, geometrical structures, and electronic population on hydrogen nuclei.