Semiempirical QM/MM method for studying HCl adsorption on ice

The combined QM/MM method, where the QM forces are obtained from a fitted PM3 semiempirical Hamiltonian, is used to study HCl adsorption at an ice surface ledge defect site. The PM3-SSP (PM3 with system-specific parameters) Hamiltonian allows for multidimensional molecular dynamics simulations that are computationally inexpensive while still providing valid reaction dynamics. The simulations reveal that, depending on the initial position of the HCl above the ledge and the number and positions of dangling surface hydrogens, adsorption may be molecular or dissociative. HCl binding energies and geometries at the ice defect site are similar to those for adsorption at crystalline hexagon sites. (C) 2003 Wiley Periodicals, Inc.