[BANANA] Berkeley Lab - Scientific Computing Seminar, September 29, 2006

[Parry Husbands]

Date: Friday, September 29, 2006
Time: 1:00pm-2:00pm
Location: Building 50A-5132

Seminar Speaker: Curtis Janssen
                  Scalable Computing Research and
                  Development Department
                  Sandia National Laboratories
                  Livermore, CA
                  http://aros.ca.sandia.gov/~cljanss/

Title: Linear Dependencies in Quantum Chemistry and
        Their Affect on Accuracy

Abstract:

Advancements in computing hardware, theoretical methods, and parallel
algorithms are greatly extending the range of molecular systems that
can be treated by ab initio quantum mechanical methods. Most of these
methods employ the linear combination of atomic orbital approach, where
a nonorthogonal basis of atom-centered Gaussian-type functions is used
to represent electronic orbitals. As either the size of the molecular
system increases (the number of atoms, each carrying a fixed number of
basis functions, grows) or the accuracy of the quantum mechanical method
increases (the number of basis functions per atoms grows), the severity of
near linear dependencies in the basis set increases. This results in  
numerical
difficulties causing slow or non-convergence, unless the basis set size is
reduced. However, automated reduction of the basis set size engenders  
altered
answers and a non-continuous potential energy surface. In this talk these
issues will be analyzed and their affect on practical computations will be
illustrated.

Sponsor of Seminar: Juan Meza