Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Amit Sharma Project Name: HPCC Division: CSE Project title: Ab-initio chemical kinetics study of high pressure combustion: A theoretical study of the radical-complex mechanism. Associated funding: Department of Energy Other Systems: Two small clusters (named: Pople and Linus) in the CSE fundamental interaction theory group. Science: Experimental investigation of the falloff curve for methyl radical oxidation, high-pressure addition reaction experiment of CCl3 with Br and benzyl radical self-addition show unexpected rise in rate constant at high pressures. In case of methyl oxidation the reaction is pressure dependent and high-pressure limit is achieved around 100 bar. Above 300 bar and in the 300 to 400 K temperature range, contribution from the radical-complex (RC) mechanism in addition to the usual energy-transfer (ET) mechanism is believed to be the dominant factor for this phenomena. The radical-complex mechanism, which has not been theoretically studied and quantified, is the formation of the radical-bath gas (R-M) complex and the stabilization/complexation is related to the strength of the R-M bond in the van der Waals complexes. The decomposition of this R-M complex to stabilized reactants yields an increase in the net association rate. Recently we have concluded the first part of our research in which we derived the rate expression for calculating radical-complex reaction rates. We developed codes to compute reaction rates at high-pressures. Project description: Following the conclusion of our CH3+O2 study (journal paper in preparation), we wish to test our theory on other systems such as CCl3+Br reaction and benzyl+benzyl reaction. These two reactions show similar high-pressure rise in rate coefficient. CCl3+Br is challenging due to spin-orbit effects. The addition reaction has 12 spin orbit electronic states of which two are attractive. We plan to calculate high pressure limiting rate on the ground spin-orbit electronic state using variable reaction coordinate transition state theory (VRC-TST). The VRC-TST calculations are expensive due to direct Monte-Carlo transition mode integrals. We compute, on-the-fly, multi reference electronic structure energies at CASPT2/aug-cc-pVDZ level of theory for sampled molecular configuration at a fixed value of reaction coordinate. In order to fit a full dimensional potential energy surface we compute thousands of such configurations spanning a multi-dimensional configuratio n space. We use MOLPRO code package for electronic structure energies. The VRC-TST code used for the calculation of reaction rate has been developed locally. The electronic structure dataset for fitting analytical PES consists of 40,000 to 50,000 electronic structure calculations for each pair of reactants. The computational cost of each electronic calculation depends on the size of the basis set, electronic structure methods and other auxiliary routines such as integral calculations and i/o routines. This can vary anywhere between 0.5 hours to couple of hours for a single point calculation, for the system we propose to study. There will be 1 to 2 people working on this project who will be using the computational resources. About 20% of the allocation will use non-parallel computations. This year we will work on CCl3+Br system and on benzyl+benzyl reaction. Benzyl is a resonance-stabilized structure and benzyl+benzyl addition reaction could require many cpu-hours. A 10 electron 6 orbital MCSCF/CASPT2/DZ test calculation, for example, requires few thousands of seconds on Pople cluster (quad core AMD opteron 1.1GHZ). However, any serious attempt to compute rate constant for this reaction would require use of a larger basis and perhaps a larger active space. We anticipate the need for longer cpu-hours especially for benzyl+benzyl reaction. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 200000 Q1: 50000 Q2: 50000 Q3: 50000 Q4: 50000 Justification: Thank You, The LCRC Accounts System