Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Marco Verdicchio Project Name: LowF_VRC-TST Division: CSE Project title: Low frequencies modes coupling in Variable Reaction Coordinate TST Associated funding: DOE-BES Other Systems: pople.tcg.anl.gov, linus.tcg.anl.gov Science: Radical-radical association reactions and unimolecular dissociations to free radicals are known to be of great importance in the chemistry of hydrocarbons combustion and planetary atmospheres. This kind of reactions, however, often show very low or absent local potential energy barrier, which makes traditional Transition State Theory (TST) calculations unfeasible. The variable reaction coordinate (VRC) TST approach has been proven to be of considerable utility in estimating the kinetic of barrierless reactions. The transition state dividing surface, defined by a fixed distance between a set of pivot points on each fragment, provide a valuable approximate division of the phase space into reactants and products. The position of each pivot in the molecular frame of the corresponding fragment determines the shape of the dividing surface. The optimization of both pivot point locations and distances between them provides a great flexibility in the definition of the dividing surface and allow the investigation of multiple binding sites system (i.e. addition reactions of resonantly stabilized, multiple side attack radical additions, etc.). A common problem for reactions involving radicals is the presence of a low frequency umbrella mode that is poorly treated in the harmonic oscillator approximation. Moreover this mode is often coupled to torsional modes and it is not clear how this coupling affect the partition functions. Our goal, in this project, is to develop and apply a new computational method to efficiently handle the large anharmonicities arising in molecule with strong coupled low frequencies modes. We propose to explore these issues for a number of prototypical radical-radical association reactions relevant in combustion and atmospheric chemistry. Project description: - Computational methods: We intend to use VRC-TST theory to study the effect of coupled low frequencies motions on EJ-resolved, microcanonical and canonical kinetic constants for several radical-radical association reactions. The central focus of VRC-TST is the evaluation of the reactive flux through an arbitrary dividing surface for several temperatures. In particular a multifaceted dividing surface approach, which allow for the incorporation of multiple dividing surfaces for each binding site, will be adopted. This scheme allows high flexibility on the dividing surface shape and the possibility to take into account additional reaction pathways (i.e. H atom abstraction). Unfortunately the computational cost of each kinetic calculation increases with the number of considered dividing surfaces. A variational minimization of the reactive flux is then performed with respect to both the location of the pivot points and the distances between them. The previous allocation let us to investigate the low-frequencies effect on the rate constants for several systems: - CH3 + H - CH3 + CH3 - CH2CH3 + H - CH2CH3 + CH3 - H + CH2OH with excellent results. The Blues machine has been found to be of great help for this type of studies allowing us to use a large number of processors (128 cpu for an average of 24h per job) and speed up considerably our calculations. In this second stage of the project, we would like to move our attention to different systems like: - CH3 + CH2OH - H + CH2OH These systems, in fact, have been already investigated within the previous allocation, but the complexity of their potential energy surface require additional work in order to work out an accurate rate constant (the low-freq effect has a strong dependence on the potential energy surface). Moreover the extension of this method to oxygenated systems: - O2 + CH3 - O2 + CH2CH3 requires the use of high level ab initio calculations (because of the presence of the O2 molecule) which are highly computationally demanding. - Technical details: Kinetic calculations will be performed using the VRC-TST method as implemented in the computer code VaReCoF (Y. Georgievskii, S.J. Klippenstein, VaReCoF, Sandia National Laboratories and Argonne National Laboratory, 2006). The code makes use of the MOLPRO or GAUSSIAN quantum chemistry software for on-the-fly evaluation of the potential energy. A Python interface to the code has been implemented for the management of the input files (reference energy evaluation, pivot points positions, etc.), for the generation of the input different structures ([Phi,Chi] grid of points) and for results post processing. The code does not require large amount of memory (less than 1GB) and works very efficiently on parallel architectures. The code makes use of MPI and shows a speed-up efficiency of about 60% for up to 96 CPU’s (test performed on a 8 cpu/cores AMD Operton 2354 machine). Improvement is expected with better CPUs and fastest internode connections. - Expected number of project members: 3 Industry partnership: Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 100000 Q1: 25000 Q2: 25000 Q3: 25000 Q4: 25000 Justification: Storage requirements: Thank You, The LCRC Accounts System