Modified genetic algorithm to model crystal structures. II. Determination of a polymorphic structure of benzene using enthalpy minimization

The Modified Genetic Algorithm scheme, presented in Paper I to model crystal structures in organic compounds (MGAC), is applied here to test its performance in the determination of a polymorphic crystalline structure of benzene that has been observed at 25 Kbar. This polymorph, named here benzene II, is not a global minimum of the energy or even close to any of the local minimum determined using the energy evolution of benzene structures described in the previous paper. The benzene II structure corresponds to an enthalpy minimum. This paper shows that it is possible to use the MGAC procedure, modified to use the minimization of the enthalpy instead of the energy in the GA (Genetic Algorithm) selection process, to find this high pressure structure of benzene. (C) 2002 American Institute of Physics.