title: Crystal structure prediction for cyclotrimethylene trinitramine (RDX) from first principles.
abstract: Crystal structure prediction and molecular dynamics methods were applied to the cyclotrimethylene trinitramine (RDX) crystal to explore the stability rankings of various polymorphs using a recently developed nonempirical potential energy function that describes the RDX dimer interactions. The energies of 500 high-density structures resulting from molecular packing were minimized and the 14 lowest-energy structures were subjected to isothermal-isostress molecular dynamics (NsT-MD) simulations. For both crystal structure prediction methods and molecular dynamics simulations, the lowest-energy polymorph corresponded to the experimental structure; furthermore, the lattice energy of this polymorph was lower than that of the other polymorphs by at least 1.1 kcal mol(-1). Crystal parameters and densities of the low-energy crystal produced by the NsT-MD simulations matched those of the experimental crystal to within 1% of density and cell edge lengths and 0.01 degrees of the cell angle. The arrangement of the molecules within the time-averaged unit cell were in equally outstanding agreement with experiment, with the largest deviation of the location of the molecular mass centers being less than 0.07 A and the largest deviation in molecular orientation being less than 2.8 degrees . NsT-MD simulations were also used to calculate crystallographic parameters as functions of temperature and pressure and the results were in a reasonable agreement with experiment.
authors: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors: Rafal
authors: R
authors: Podeszwa
authors: Betsy M
authors: BM
authors: Rice
authors: Krzysztof
authors: K
authors: Szalewicz
mesh_terms: D003198:Computer Simulation; D003460:Crystallization; D013816:Thermodynamics; D014227:Triazines / Q000737:chemistry*
chemical_list: D014227:Triazines; C009160:cyclonite