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Title: Chemistry and Beyond : the tale of a surface chemist.


No abstract prepared.

Publication Date:
Research Org.:
Sandia National Laboratories
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Report Number(s):
TRN: US200906%%243
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Conference: Proposed for presentation at the Abilene Christian University Math and Science Centennial Conference held January 27-28, 2006 in Abilene, TX.
Country of Publication:
United States

Citation Formats

Ohlhausen, James Anthony. Chemistry and Beyond : the tale of a surface chemist.. United States: N. p., 2006. Web.
Ohlhausen, James Anthony. Chemistry and Beyond : the tale of a surface chemist.. United States.
Ohlhausen, James Anthony. Sun . "Chemistry and Beyond : the tale of a surface chemist.". United States. doi:.
title = {Chemistry and Beyond : the tale of a surface chemist.},
author = {Ohlhausen, James Anthony},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}

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  • Abstract not provided.
  • One of the most prominent aims in Computational Chemistry is the modeling of chemical reactions and the prediction of molecular properties. Quantum chemical methods are used for the calculation of molecular structures, spectra, reaction energy profiles and many other interesting quantities. Nowadays, the accuracy of the theoretical calculations can compete to an increasing extent with the experimental one. A great variety of quantum chemical methods exist ranging from the standard Hartree-Fock theory to sophisticated electron correlation approaches. From a computational point of view all these methods require rather lengthy and complicated program codes and have to handle a large amountmore » of data to be stored on external devices. In the simplest case, the Hartree-Fock (SCF) method, ``direct`` algorithms have eliminated the I/O and storage bottleneck and have opened the way to parallel implementations. For post-Hartree-Fock methods the situation is much more complicated as will be demonstrated below. Therefore, most of the previous attempts in parallelizing quantum chemical ab initio programs concentrated on SCF methods. The authors investigations presented here are a continuation of their previous work on the parallelization of the COLUMBUS program system. The COLUMBUS program is based on the multireference single- and double-excitation configuration interaction (MRSDCI) approach. It is very portable and runs on a large variety of computers including numerous Unix-based workstations, VAX/VMS minicomputers, IBM mainframes and Cray supercomputers.« less
  • One of the most important challenges in chemistry is to develop predictive ability for the branching between energetically allowed chemical reaction pathways. Such predictive capability, coupled with a fundamental understanding of the important molecular interactions, is essential to the development and utilization of new fuels and the design of efficient combustion processes. Existing transition state and exact quantum theories successfully predict the branching between available product channels for systems in which each reaction coordinate can be adequately described by different paths along a single adiabatic potential energy surface. In particular, unimolecular dissociation following thermal, infrared multiphoton, or overtone excitation inmore » the ground state yields a branching between energetically allowed product channels which can be successfully predicted by the application of statistical theories, i.e. the weakest bond breaks. (The predictions are particularly good for competing reactions in which when there is no saddle point along the reaction coordinates, as in simple bond fission reactions.) The predicted lack of bond selectivity results from the assumption of rapid internal vibrational energy redistribution and the implicit use of a single adiabatic Born-Oppenheimer potential energy surface for the reaction. However, the adiabatic approximation is not valid for the reaction of a wide variety of energetic materials and organic fuels; coupling between the electronic states of the reacting species play a a key role in determining the selectivity of the chemical reactions induced. The work described below investigated the central role played by coupling between electronic states in polyatomic molecules in determining the selective branching between energetically allowed fragmentation pathways in two key systems.« less
  • We present recent advances with the quantum Monte Carlo (QMC) method in its application to molecular systems. The QMC method is a procedure for solving the Schroedinger equation statistically, by the simulation of an appropriate random process. The formal similarity of the Schroedinger equation with a diffusion equation allows one to calculate quantum mechanical expectation values as Monte Carlo averages over an ensemble of random walks. We have previously obtained highly accurate correlation energies for a number of molecules, as well as the singlet-triplet splitting in methylene and the barrier height for the H + H/sub 2/ exchange reaction. Recentlymore » we have begun a program of extending the QMC approach to the calculation of analytic derivatives of the energy. A brief description of the approach is presented here, together with some preliminary results. In addition, we are now computing expectation values of properties other than the energy. We summarize how standard QMC must be modified, and present some results for H/sub 2/ and N/sub 2/. Finally, we describe preliminary work toward the goal of obtaining accurate molecular excited states through QMC. 24 refs., 5 tabs.« less