Ab initio molecular dynamics simulations of the adsorption of the methylguanidine or methylguanidinium on Ag(111)

A density-functional and Car–Parrinello molecular dynamics methods were employed to study the adsorption of the methylguanidine or methylguanidinium on Ag(111) surface with Vanderbilt pseudopotentials and PBE functional. The geometry, interacting energy, vibrational frequency, Mayer bond order and electrostatic fit charges were calculated. The results show that the methylguanidine interacts with the Ag(111) surface mainly through the interaction between the sp² hybridisation imine nitrogen and its nearest silver atom on top site, assisted with the Ag???H interaction, with the most stabilising interacting energy ?78.83 kJ/mol. The Car–Parrinello molecular dynamics results at 293.15 or 300.00 K indicate that the Ag???N interaction exists stably for more than 6 ps and the Mayer bond order analysis shows that it is the main interaction in adsorption. For the methylguanidinium on Ag(111) surface, the weak interaction between N?H and its neighbour silver atoms, with the energy of ?40.73–?42.68 kJ/mol and the interacting time of 0.2–0.3 ps at 300 K, could not keep it steady on Ag(111). The CP dynamics results show that only the methylguanidine could adsorb on Ag(111) at the room temperature.