Development of a ReaxFF Force Field for Cu/S/C/H and Reactive MD Simulations of Methyl Thiolate Decomposition on Cu (100).

It has been shown that the rate of decomposition of methyl thiolate species on copper is accelerated by sliding on a methyl thiolate covered surface in ultrahigh vacuum at room temperature. The reaction produces small gas-phase hydrocarbons and deposits sulfur on the surface. Here, a new ReaxFF potential was developed to enable investigation of the molecular processes that induce this mechanochemical reaction by using density functional theory calculations to tune force field parameters for the model system. Various processes, including volumetric expansion/compression of CuS, CuS2, and Cu2S unit cells; bond dissociation of Cu-S and valence angle bending of Cu-S-C; the binding energies of SCH3, CH3, and S atoms on a Cu surface; and energy for the decomposition of methyl thiolate molecular species on copper, were used to identify the new ReaxFF parameters. Molecular dynamics simulations of the reactions of adsorbed methyl thiolate species at various temperatures were performed to demonstrate the validity of the new potential and to study the thermal reaction pathways. It was found that reaction is initiated by C-S bond scission, consistent with experiments, and that the resulting methyl species diffuse on the surface and combine to desorb ethane, also as found experimentally.

Ethnic related variations from the cass model of homosexual identity formation: the experiences of two-spirit, lesbian and gay Native Americans.

Synthesis of current research with the self-stories of Native American two-spirit, lesbian and gay people suggests differences in social locations that may produce sexual orientation identity development processes absent from the current literature. We employed a modified form of grounded theory analysis to explore the identity experiences of six self-identified two-spirit, lesbian or gay Native Americans recounted during in-depth interviews. The resulting five themes are presented with quotes from participants for clarification and support, along with a discussion of their fit with the Cass Model of Homosexual Identity Development and interpersonal congruency theory. Results suggest two developmental pathways, one following the course of Cass' model and a second path notable for its absence of many of the key experiences specified by Cass.