Hello,
A change in allocation has been requested:
Requester: verdicm (Marco Verdicchio)
Project: LowF_VRC-TST
Title: Low frequencies modes coupling in Variable Reaction Coordinate TST
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.
In this first stage of the project*, the following systems will be taken into consideration:
- C2H5 + H
- CH3 + CH3
- CH3 + CH2OH
- C2H5 + O2
(*Extension and optimization of the method for larger chemical systems is also a crucial point.)
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.
In order to evaluate the effect of the coupling of the two low frequencies modes on the kinetic constant we will compute the reactive flux for different values of torsional angle (Phi) and umbrella bending (Chi). This step requires the generation of a large set of independent VRC-TST kinetic calculations one for each value of the couple [Phi, Chi]. The final kinetic constant is then obtained by integrated (with proper weight functions for each point) over Phi and Chi. To provides a suitable description of the torsional and umbrella motion potentials, and to include Complete Basis Set limit corrections to the potential energy, preliminary quantum chemistry ab initio calculations are also necessary (about 10000 cpu/hours).
- 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
Current: undetermined amount
Justification:
Requested: 60000
A specific reason has been given:
We have decided to extent our calculations to other bigger chemical system and this requires the use of additional cpu hours. Moreover because of initial problems in the setting up of the computational procedure we didn't consume about 25k cpu hour from the first allocation (these hours were cancelled because of the end of the first quarter). Now our code is working and it gives good performances on the BLUES machine (as confirmed by the consumption of the second quarter cpu hours before the end of the expected end of the quarter).
This needs to be approved and the final allocation amount decided upon.
Thank You,
The LCRC Accounts System
