Niranjan Govind

A generalized synchronous transit method for transition state location

Abstract This paper describes a generalized synchronous transit method for locating transition state structures or first-order saddle points. The algorithm is based on the established scheme of combining the linear or quadratic synchronous transit method with conjugate gradient refinements but generalized to deal with molecular and periodic systems in a seamless manner. We apply the method to a study of the early stage atomic layer deposition (ALD) growth of ZrO2.

Effect of surface phosphorus on the oxidative dehydrogenation of ethane: A first-principles investigation

Oxidative dehydrogenation (ODH) of small-chain alkanes has the potential to displace thermal cracking as the preferred method of light olefin production. Many heterogeneous catalysts for the ODH reaction have been discussed in the literature, including oxides, vanadates, and phosphates of rare earth and transition metals. Our experiments and the literature indicate that for most of these catalysts, including silica gel and alumina, a phosphorus-enriched surface enhances the ODH yield of ethane to ethylene. To understand the role of P, the ODH reactions were simulated on a silica surface, with and without P, using the density functional theory code DMol3 in a periodic supercell. Optimized structures for all intermediates as well as transition states were obtained for full catalytic cycles. The simulations reveal that activation barriers for the rate-limiting steps are lowered by ∼10 kcal/mol in the presence of P. The decrease results from a transition state in which the P atom remains quasi-5-valent and fo...