Julio Facelli

Project Title:
Modeling 13-C and 15-N Chemical Shifts in Crystalline systems.
Contact Person(s) (Individual, Institution, city, country, email) :
Dr Julio C. Facelli
Director
UNIVERSITY OF UTAH
CTR FOR HIGH PERFORM COMPUTING
155 SOUTH 1452 EAST RM 405
SALT LAKE CITY UT 84112-0190
Phone (801)-581-7529
Fax (801)-585-5366
e-mail facelli@chpc.utah.edu

Potential Collaborators (including contact people) (Individual, Institution, city, country, email) :
Dr. Marta Ferraro
Departamento de Fisica
Universidad de Buenos Aires
1428 Buenos Aires Argentina
marta@dfuba.df.uba.ar

Project URL (if one exists) :
n/a
Application Description (1-2 paragraphs):
Nuclear Magnetic Resonance (NMR) spectroscopy is one of the most important tools for characterizing the structure of organic, biological macromolecules and inorganic materials. Increasingly, researchers use solid state NMR to characterize great variety microscopic structures. A common complication of NMR spectra in solid state is the duplication of lines corresponding to formally magnetically equivalent nuclei due to intermolecular or crystalline effects. Conversely, if properly modeled, these minor deviations from the corresponding liquid spectrum may be used to investigate details in the crystalline structure and to remove ambiguities in the assignment of lines in the NMR solid state spectra. Computer hardware and software have reached the point that modeling these effects may be an achievable goal. Existing quantum mechanical methods in use to predict NMR nuclear shielding do not use crystalline wave functions to evaluate the shift tensor components; consequently, the theoretical results do not include any intermolecular contributions to the shielding.
This proposal request supplemental funding to accelerate the collaboration between the NMR research groups at the University of Utah and Universidad de Buenos Aires (Argentina). These groups are developing computational tools to model the intermolecular effects observed on the NMR chemical shieldings measured in the solid state. The combined expertise and resources of these two groups have the potential to make significant faster progress in this field.

The calculation of chemical shielding in systems of real interest with periodic boundary conditions, will require calculations in crystals with more than 30-40 atoms in the unit cell. We anticipate needing a great deal of computer power. All the code develop will use, as much as possible, parallel computer techniques. We will use the MPI standard to make the code highly portable to different parallel architectures available at the Center for High Performance Computing. Several of the molecules that have been studied by the Utah group in detail (naphthalene, benzamide, pyrene, imidazole, etc.) will be used to test the accuracy of the methods develop here. The PIs are familiar with the NMR as well as the high quality diffraction data existing for these molecules.
Finally, we will try to use the new software developed under this program to further explore the use of NMR as a tool for quantitative structural elucidation when diffraction data may not be available. To this end this program could be used as intermediate to correlate crystal geometry and chemical shifts. When this feature is added to a crystal modeling program, it will be possible to use the experimental NMR chemical shifts as additional constrains to the optimization of the crystal structure. These techniques have been used extensively with NOEs and J couplings (Karplus type of equations) to solve molecular structures in liquids. The missing link to use the same approach in solids using the NMR chemical shifts is a robust method to calculate the nuclear shielding in crystalline systems.

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