Our work on AIMD simulation of CL-20 thermal decomposition just get published in the J. Phys. Chem. B!

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane or HNIW) is a high-energy nitramine explosive. To improve atomistic understanding of the thermal decomposition of CL-20 gas and solid phases, we performed a series of ab initio molecular dynamics simulations. We found that during unimolecular decomposition, unlike other nitramines (e.g., RDX, HMX), CL-20 has only one distinct initial reaction channel—homolysis of the N—NO₂ bond. We did not observe any HONO elimination reaction during unimolecular decomposition, whereas the ring-breaking reaction was followed by NO₂ fission. Therefore, in spite of limited sampling, that provides a mostly qualitative picture, we proposed here a scheme of unimolecular decomposition of CL-20. The averaged product population over all trajectories was estimated at four HCN, two to four NO₂, two to four NO, one CO, and one OH molecule per one CL-20 molecule. Our simulations provide a detailed description of the chemical processes in the initial stages of thermal decomposition of condensed CL-20, allowing elucidation of key features of such processes as composition of primary reaction products, reaction timing, and Arrhenius behavior of the system. The primary reactions leading to NO₂, NO, N₂O, and N₂ occur at very early stages. We also estimated potential activation barriers for the formation of NO₂, which essentially determines overall decomposition kinetics and effective rate constants for NO₂ and N₂. The calculated solid-phase decomposition pathways correlate with available condensed-phase experimental data.

Isayev, O., Gorb, L., Qasim, M., Leszczynski, J. (2008). Ab Initio Molecular Dynamics Study on the Initial Chemical Events in Nitramines: Thermal Decomposition of CL-20. Journal of Physical Chemistry B, 112(35), 11005-11013. DOI: 10.1021/jp804765m

28th August, 2008 No Comments

As a first New Year gift, our work on calculation of ?G for intermolecular complexes has been published in Chemical Physics Letters!

Recently proposed protocol for accurate (errors within about 1 kcal/mol of experimental data) prediction of the thermodynamic parameters of intermolecular interactions have been tested against other DFT, MP2 and CCSD(T) based methods for complexes including GC and AT DNA base pairs. Newly optimized procedure comprising of two steps proved itself as good compromise between computational demand and chemical accuracy. The first step of proposed protocol involves the counterpoise corrected optimization and calculation of harmonic frequencies at B3LYP/cc-pVTZ level. The second step consists of single point MP2 (cc-pVDZ and cc-pVTZ) calculations and extrapolation to the complete basis set limit.

ISAYEV, O., FURMANCHUK, A., GORB, L., LESZCZYNSKI, J. (2008). Efficient and accurate ab initio prediction of thermodynamic parameters for intermolecular complexes. Chemical Physics Letters, 451(1-3), 147-152. DOI: 10.1016/j.cplett.2007.11.079

2nd January, 2008 1 Comment