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Parish, Carol A.

Publications and source records attributed to Parish, Carol A..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Experimental and Theoretical Study of Oxolan-3-one Thermal Decomposition

The thermal decomposition of oxolan-3-one, a common component of the bio-oil formed during biomass pyrolysis, has been studied using ab initio calculations and experiments employing pulsed gas-phase pyrolysis with matrix isolation FTIR product detection. Four pathways for unimolecular decomposition were predicted using computational methods. The dominant reaction channel led to carbon monoxide, formaldehyde, and ethylene, all of which were observed experimentally. Here, the other channels led to an assortment of products including ketene, water, propyne, and acetylene, which were all confirmed in the matrix-isolation FTIR spectra. There is also evidence for the production of substituted ketenes in pyrolysis, most likely hydroxyketene and methylketene.

09 BIOMASS FUELS↗
DOE OSTI2020

The Generality of the GUGA MRCI Approach in COLUMBUS for Treating Complex Quantum Chemistry

The core part of the program system COLUMBUS allows highly efficient calculations using variational multireference (MR) methods in the framework of configuration interaction with single and double excitations (MR-CISD) and averaged quadratic coupled-cluster calculations (MR-AQCC), based on uncontracted sets of configurations and the graphical unitary group approach (GUGA). The availability of analytic MR-CISD and MR-AQCC energy gradients and analytic nonadiabatic couplings for MR-CISD enables exciting applications including, e.g., investigations of π-conjugated biradicaloid compounds, calculations of multitudes of excited states, development of diabatization procedures, and furnishing the electronic structure information for on-the-fly surface nonadiabatic dynamics. With fully variational uncontracted spin-orbit MRCI, COLUMBUS provides a unique possibility of performing high-level calculations on compounds containing heavy atoms up to lanthanides and actinides. Crucial for carrying out all of these calculations effectively is the availability of an efficient parallel code for the CI step. Configuration spaces of several billion in size now can be treated quite routinely on standard parallel computer clusters. Emerging developments in COLUMBUS, including the all configuration mean energy multiconfiguration self-consistent field method and the graphically contracted function method, promise to allow practically unlimited configuration space dimensions. Spin density based on the GUGA approach, analytic spin-orbit energy gradients, possibilities for local electron correlation MR calculations, development of general interfaces for nonadiabatic dynamics, and MRCI linear vibronic coupling models conclude this overview.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗