First-principle calculation on isotope effect in KH2PO4 and KD2PO4 of hydrogen-bonded dielectric materials.: Approach with dynamic extended molecular orbital method

We have theoretically rationalized the origin of the isotope effect on phase transition temperature in hydrogen-bonded ferroelectric materials, KH2PO4 and KD2PO4 , using the new first-principle dynamic extended molecular orbital (DEMO) method, which can determine both electronic and nuclear wave functions simultaneously. We confirm that the origin of the isotope effect is the localization of the nuclear wave function by deuterization. The DEMO method has also universally demonstrated the isotope effect in potential energies, geometrical structures, and electronic population on hydrogen nuclei.