Many-Fermion Dynamics---nuclear, or MFDn, is a configuration interaction (CI) code for nuclear structure calculations. It is a platform independent Fortran 90 code using a hybrid MPI/ OpenMP* programming model, and is being used on current supercomputers, such as Edison at NERSC, for ab initio calculations of atomic nuclei using realistic nucleon-nucleons and three-nucleon forces. A calculation consists of generating a many-body basis space, constructing the many-body Hamiltonian matrix in this basis, obtaining the lowest eigenpairs, and calculating a set of observables from those eigenpairs. Key computational challenges for MFDn include effectively using the available aggregate memory, efficient construction of the matrix, and efficient sparse matrix--vector products used in the solution of the eigenvalue problem.
To accurately capture this need NERSC developed a test code which uses representative data for production calculations on 5,000 Intel® Xeon Phi™ processors nodes (approximately half the size of Cori at NERSC) using over 80~GB of memory per node.