Extended Lagrangian Born-Oppenheimer molecular dynamics simulations of the shock-induced chemistry of phenylacetylene

Abstract

The initial chemical events that occur during the shock compression of liquid phenylacetylene have been investigated using self-consistent tight binding molecular dynamics simulations. The extended Lagrangian Born-Oppenheimer molecular dynamics formalism enabled us to compute microcanonical trajectories with precise conservation of the total energy. Our simulations revealed that the first density-increasing step under shock compression arises from the polymerization of phenylacetylene molecules at the acetylene moiety. The application of electronic structure-based molecular dynamics with long-term conservation of the total energy enabled us to identify electronic signatures of reactivity via monitoring changes in the HOMO-LUMO gap, and to capture directly adiabatic shock heating, transient non-equilibrium states, and changes in temperature arising from exothermic chemistry in classical molecular dynamics trajectories.

Examining the chemical and structural properties that influence the sensitivity of energetic nitrate esters

“…Following the thermalization of the three derivatives to set the initial temperature, we switched to microcanonical dynamics in order to allow the temperature to evolve with onset of endo- and exothermic chemistry. 49 Precise, long-term conservation of the total energy during microcanonical dynamics was obtained using the extended Lagrangian Born-Oppenheimer MD formalism of Niklasson et al 50 Each simulation was run for ∼200 ps until they had decomposed into product species. The evolution of the interatomic bonding was computed by post-processing the stored trajectories.…”

Extended Lagrangian Formulation of Charge-Constrained Tight-Binding Molecular Dynamics

“…Upon taking the limit μ → 0, we recover the regular equations of motion for the atoms (13) and an equation of motion for the auxiliary degrees of freedom…”

Equilibrium configurations of large nanostructures using the embedded saturated-fragments stochastic density functional theory

“…One primary direction is based on a Lagrangian formulation of density functional theory 1,11 and circumvents the need for SCF iterations by propagation of the KS orbitals. This venue does not eliminate the cubic scaling and is therefore limited to relatively small systems.…”

“…[1][2][3][4][5][6][7][8][9][10][11] The application of this approach to very large systems is still limited by the computational scaling of the electronic structure portion of the calculation, regardless of whether one uses a Lagrangian-based or Born-Oppenheimer-based methods. This is because of the cubic scaling involved in solving the Kohn-Sham equations coupled with the need to iterate to self-consistency or to propagate the Kohn-Sham (KS) orbitals, as both of these options further increases the computational times by an order of magnitude.…”