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

Abstract

We have theoretically elucidated the origin of the isotope effect on phase transition temperature in hydrogen-bonded ferroelectric materials K 3 H(SO 4 ) 2 and K 3 D(SO 4 ) 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 effective potential energies, geometrical structures, and electronic population on hydrogen nuclei.Keywords: isotope effect on phase transition temperature, hydrogen-bonded ferroelectric material, geometrical isotope effect, K 3 H(SO 4 ) 2 and K 3 D(SO 4 ) 2 , multi-component molecular orbital method, Ubbelohde effect

Theoretical study of the H/D isotope effect on phase transition of hydrogen-bonded organic conductor κ-H3(Cat-EDT-TTF)2

“…DKHS has a finite phase transition temperature (T C = 85 K), while KHS shows no phase transition (T C o 0 K). [17][18][19] We have already demonstrated the significant H/D isotope effect on the structures and the effective potential energies for KHS and DKHS, that is, the single minimum effective potential energy was obtained for KHS while double minima for DKHS. 17 Recently, Mori et al have newly developed a H-bonded molecularunit-based organic conductor crystal, k-H 3 (Cat-EDT-TTF) 2 (abbreviated to H-TTF), whose novelty lies in the fused structure of short H-bonds and stacked p-electron systems.…”

“…[17][18][19] We have already demonstrated the significant H/D isotope effect on the structures and the effective potential energies for KHS and DKHS, that is, the single minimum effective potential energy was obtained for KHS while double minima for DKHS. 17 Recently, Mori et al have newly developed a H-bonded molecularunit-based organic conductor crystal, k-H 3 (Cat-EDT-TTF) 2 (abbreviated to H-TTF), whose novelty lies in the fused structure of short H-bonds and stacked p-electron systems. H-TTF consists of two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons linked by a symmetric anionic [OÁ Á ÁHÁ Á ÁO] À1 -type strong H-bond as shown in Fig.…”

“…DKHS has a finite phase transition temperature ( T C = 85 K), while KHS shows no phase transition ( T C < 0 K). 17–19 We have already demonstrated the significant H/D isotope effect on the structures and the effective potential energies for KHS and DKHS, that is, the single minimum effective potential energy was obtained for KHS while double minima for DKHS. 17…”

“…[8][9][10][11][12][13] Such a quantum effect appears especially in the difference between the behaviors of the light and heavy hydrogen nuclei, which is known as the H/D isotope effect. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Since the quantum fluctuation of deuterium is significantly different from that of light hydrogen due to the heavier mass, the deuterium substitution of H-bonds often causes significant differences in the structures and physical properties. For instance, K 3 H(SO 4 ) 2 (KHS) and K 3 D(SO 4 ) 2 (DKHS) have a unique character with respect to phase transition.…”