  We describe a number of recently developed techniques for improving the
performance of large-scale nuclear configuration interaction calculations on
high performance parallel computers. We show the benefit of using a
preconditioned block iterative method to replace the Lanczos algorithm that has
traditionally been used to perform this type of computation. The rapid
convergence of the block iterative method is achieved by a proper choice of
starting guesses of the eigenvectors and the construction of an effective
preconditioner. These acceleration techniques take advantage of special
structure of the nuclear configuration interaction problem which we discuss in
detail. The use of a block method also allows us to improve the concurrency of
the computation, and take advantage of the memory hierarchy of modern
microprocessors to increase the arithmetic intensity of the computation
relative to data movement. We also discuss implementation details that are
critical to achieving high performance on massively parallel multi-core
supercomputers, and demonstrate that the new block iterative solver is two to
three times faster than the Lanczos based algorithm for problems of moderate
sizes on a Cray XC30 system.
