Background Science Applications Physics Climate Groundwater Fusion Energy Life Sciences Materials & Chemistry SciDAC Institutes Collaboratories Enabling Technologies Applied Mathematics Computer Science Visualization & Data Mgt. SciDAC Outreach Participating Orgs Grant Solicitations FY2007 FY2006 FY2005 FY2004 FY2001 Collateral Materials SciDAC Review magazine '06 Progress Report (pdf) Publications 2001-5 (pdf) Logos Search Collateral (from SciDAC 1) Browse by Affiliation Browse by Author Browse by Title DOE Office of Advanced Scientific Computing Research (ASCR) Program Managers only

Development Of New Scalable Multi-Reference Solutions For Electronic Structure, Dynamics and Non-Equilibrium Statistical Mechanics of Complex Reaction Processes

PI

Mark S. Gordon, Iowa State University and Ames Laboratory

Co-PIs

• Professor James W. Evans, Iowa State University and Ames Laboratory
• Professor Klaus Ruedenberg, Iowa State University and Ames Laboratory
• Dr. Michael W. Schmidt, Ames Laboratory

Affiliated Researchers

• Professor Piotr Piecuch, Department of Chemistry, Michigan State University
• Professor Brett M. Bode, Iowa State University and Ames Laboratory
• Professor Ricky A. Kendall, Iowa State University and Ames Laboratory
• Dr. Graham Fletcher, NASA Ames Research Center
• Dr. Joseph Ivanic, National Cancer Institute

Summary

The focus of this research is to develop new models for investigating the details of the mechanisms of chemical reactions for complex systems, including biomolecular processes and surface phenomena, including heterogeneous catalysis. The ability to study "extended" systems, containing tens to thousands of atoms, with reasonable accuracy is of paramount importance. The development of methods to adequately treat such systems requires highly scalable, highly correlated electronic structure methods interfaced with classical methods and mesoscale codes.

Recent Accomplishments

All of the new developments of scalable electron correlation methods are implemented into the electronic structure code GAMESS (General Atomic and Molecular Electronic Structure System). GAMESS is distributed at no cost and currently has a registered user base of nearly 9,000. The code is developed in such a way that it is easily implemented on any hardware and operating system. In addition to present and former members of the Gordon group, scores of colleagues all over the world contribute to the development of GAMESS, The new GAMESS developments are often shared with others, especially the developers of NWChem at PNNL. This interaction with PNNL benefits both laboratories as well as the general user community. The new developments in the past year include:

Highly scalable, distributed data and replicated data full CI (configuration interaction) codes. Full CI provides the exact wavefunction for a given atomic basis, so it represents the baseline against which the accuracy of all other calculations may be measured. Therefore, although full CI can only be applied to relatively small systems, it is extremely important to extend the size of molecules to which it can be applied. This highly scalable code is a key advance. Further, it is very common to initiate a calculation by performing a full CI in a limited part of the wavefunction (called an "active space"). Such methods are called complete active space (CAS) self-consistent field (SCF) methods. These methods can be applied to larger problems than can full CI, so the parallel full CI method also pushes forward our ability to do CASSCF calculations.

Even the CASSCF wavefunction is a highly demanding calculation. We have recently developed and implemented into GAMESS a more general multi-configurational (MC)SCF method that dramatically reduces the computational effort.

The MCSCF wavefunction often is only the starting foundation, upon which an even more sophisticated wavefunction must be built. One such wavefunction is called second order CI (SOCI). A very efficient SOCI capability has now been implemented in GAMESS.

Another very important method for electron correlation is called coupled cluster (CC), generally considered to be the state-of-the-art when MC methods are not required. A suite of CC methods for the study of ground electronic states has now been implemented.

A kinetic Monte-Carlo code was developed to describe the complex interplay between surface reaction processes and nanostructure formation during etching and oxidation of Si(100). Modeling was guided by ab-initio results for key energies.

Developments Anticipated FY03, FY04

Continuing the theme of making more efficient MC methods, a new approach (ORMAS) has been developed and will be implemented (with energy gradients) shortly. This method allows one to subdivide the active space into sets of smaller spaces, thereby greatly increasing the size of a system that can be studied.

In order to make optimal use of ORMAS, the development of higher order electron correlation methods for ORMAS, such as SOCI, will be initiated.

The CC codes in GAMESS will be broadened to include excited electronic states, in order to facilitate the study of photochemistry and photobiology. In subsequent years, open shell capabilities will be developed.

In order to optimize the efficiency of the most sophisticated methods, like SOCI, these codes will be made more scalable.

The availability of energy gradients (first derivatives) allows the user to more efficiently predict molecular geometries and to follow reaction paths. Analytic gradients will therefore be developed and implemented into GAMESS for several of the correlated methods.

Energy second derivatives (Hessians) are essential for predicting many properties, such as infrared spectra. MCSCF Hessians will be developed and implemented.

Codes will be developed that utilize kinetic Monte Carlo and other mesoscale modeling approaches to describe non-equilibrium cooperative behavior in a variety of reaction and growth processes on Si(100) surfaces. These codes will incorporate output from large-scale quantum chemistry calculations (e.g., values for key activation barriers).

Impact of Team Effort:

Nearly all of the completed and planned developments described above have benefited from interactions with colleagues within our group, in other institutions, in ISICs. The MCSCF developments are all accomplished via collaborations with the Gordon and Ruedenberg groups. The ORMAS developments are primarily due to Ivanic, the coupled cluster codes to Piecuch and co-workers. All parallel efforts benefit greatly from interactions with the Fletcher, Kendall and Bode groups. Less obvious, but equally important, are our interactions and discussions with colleagues in other DOE laboratories, especially those at PNNL.

Computational Needs:

The primary need is for significant amounts of time (on the order of 500,000 node hours/year) on the NERSC systems.

back to project page