Research Projects

An ab initio Molecular Dynamics Study of the Initial Chemical Events in CL-20^†

CL-20 or (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) † O. Isayev, L. Gorb, M. Qasim, J. Leszczynski. 2008, (Submitted).
Please also come to hear me at upcoming Spring 2008 ACS National Meeting, New Orleans, LA (April 6 – 10, 2008).belongs to the class of high-energy nitramine explosives. To improve atomistic understanding of the thermal decomposition in gas phase and bulk CL-20 we performed series of ab initio molecular dynamics simulations.

Unlike other nitramines like RDX/HMX we found only one distinct initial reaction channel (homolysis of N-NO₂ bond) during unimolecular decomposition. We did not observe any HONO elimination reaction under these circumstances. Whereas, ring breaking reaction followed by NO₂ fission. Therefore, in spite limited sampling that provide mostly qualitative picture, we proposed scheme of unimolecular decomposition of CL-20. The averaged products population over all trajectories is estimated at 4 HCN, 2—4 NO₂, 2—4 NO, ~1 CO, and ~1 OH molecule per one CL-20.

Our simulations provideSeveral animation movies are available:
Unimolecular decomposition.
(about 3 minutes, 37 Mb)
Decomposition in crystal CL-20.
(about 1 minute, 13 Mb)
First movie has been featured on AHPCRC booth at SC06 exposition. a detailed description of the chemical processes in the initial stages of thermal decomposition condensed CL-20. They allow us to elucidate key features of such process: composition of primary reaction products, reaction timing, Arrhenius behavior of the system, etc. They clearly indicate that the primary reactions leading to NO₂, NO, N₂O and N₂ occur at very early stages. We also estimate activation barrier for the formation of NO₂ which is essentially determines overall decomposition kinetics and effective rate constants for NO₂ and N₂. Calculated bulk decomposition pathways correlates with available condensed phase experimental data. Unfortunately, comparison of the predicted gas phase mechanism is not possible.

Structure of Liquid Water from ab initio Molecular Dynamics at the Complete Plane Wave Basis Set Limit

Water the most important liquid on Earth. Due to its critical role in many chemical and biological processes, a detailed understanding of the structural and dynamical properties of water is essential. As a result of many experimental and theoretical studies, a qualitative picture of the local solvation shell structure and dynamics of liquid water has emerged.

Unfortunately, the results obtained from different ab initio molecular dynamics (AIMD) studies of liquid water do not always agree with each other and often show disagreement with experiment. It has been even argued that the lack of agreement results from an irreproducibility of AIMD simulations of liquid water at ambient condition leading to a wide range of structural and dynamical properties.¹1.J. G. Grossman, E. Schwegler, E. W. Draeger, F. Gygi, and G. Galli, J. Chem. Phys. 120 (2004), 300.;
E. Schwegler, J. C. Grossman, F. Gygi, and G. Galli, J. Chem. Phys. 121 (2004), 5400.
2.H.-S. Lee and M. E. Tuckerman J. Chem. Phys. 125 (2006), 154507;
H.-S. Lee and M. E. Tuckerman J. Chem. Phys. 126 (2007), 164501.

Recently, this issue has been addressed by the another computational approach employing a discrete variable representation (DVR) basis set rather than plane wave basis set.² This study showed more accurate RDF values compared to earlier works.

In an effort to access this problem we performed series of AIMD very near the complete basis set limit. Comparison with the results obtained with the common setup demonstrates the effects basis set completeness on the structural and dynamic properties of liquid water.

Project two

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Morbi faucibus. Cras sit amet est quis massa posuere mollis. Nulla facilisi. Aliquam erat volutpat. Morbi dictum massa mattis velit. Mauris faucibus sem vitae urna. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Cras eget libero eget mi ultricies malesuada. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Duis commodo, odio vel tempus tempus, dui arcu posuere leo, dictum pulvinar nulla enim nec ligula. In tempor pellentesque leo.