Path integral molecular dynamics for hydrogen adsorption site of zeolite-templated carbon with semi-empirical PM3 potential

To evaluate the adsorption sites of hydrogen atom on buckybowl-like molecule (C₃₆H₁₂), which is a model fragment structure of zeolite-templated carbon (ZTC), we have performed path integral molecular dynamics (PIMD) simulation including thermal and nuclear quantum fluctuations under the semi-empirical PM3 potential. Here we have picked up ten carbons as the adsorption sites of additional hydrogen atom (H^*), which are labeled as α-, β₁-, β₂-, γ-, and δ-carbon from edge to bottom carbon for inside and outside of C₃₆H₁₂, respectively. In the static PM3 calculation and conventional MD simulation the ten stable adsorption sites of H^* are obtained both inside and outside of C₃₆H₁₂. In PIMD simulation, on the other hand, the nine stable adsorption sites are obtained, except for δ-carbon for inside of C₃₆H₁₂. This result is due to the fact that the thermal effect and zero point vibration of δ-carbon and H^* stretching motion make adsorbed hydrogen atom go over potential barrier from δ- and β₁-carbon for inside of C₃₆H₁₂ more readily. The thermal and nuclear quantum effects are important to evaluate the hydrogen adsorption site on carbon materials.