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 Comments Off

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 View Comments