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The Locally Self-consistent Multiple Scattering (LSMS) code solves the first principles Density Functional theory Kohn-Sham equation for a wide range of materials with a special focus on metals, alloys and metallic nanostructure and other materials applications. LSMS calculates the local spin density approximation to the diagonal part of the electron Green’s function. The electron/spin density and energy are easily determined once the Green’s function is known. Linear scaling with system size is achieved in the LSMS by using several unique properties of the real space multiple scattering approach to the Green’s function 1) the Green’s function is “nearsighted”, therefore, each domain, i.e. atom, requires only information from nearby atoms in order to calculate the local value of the Green’s function. 2) the Green’s function is analytic, therefore, the required integral over electron energy levels can be analytically continued onto a contour in the complex plane where the imaginary part of the energy further restricts its range; and 3) to generate the local electron/spin density an atom needs only a small about of information, phase shifts, from those atoms within the range of the Green’s function. The very compact nature of the information that needs to be passed between processors and the high efficiency of the dense linear algebra algorithms employed to calculate the Green’s function are responsible for the superior performance of the LSMS code. In addition of non relativistic and scalar relativistic calculations, LSMS allows the solution of the fully relativistic Dirac equation for electron scattering. Thus, all relativistic effects including spin-orbit interactions are accounted for, which allows the calculation of magnetocrystaline anisotropy energies and Dzyaloshinskii-Moriya antisymmetric exchange interactions. The energies for arbitrary non-collinear magnetic spin configurations can be calculated using self- consistently determined Lagrange multipliers that constrain the local magnetic order. LSMS utilizes multiple levels of parallelism: 1) distributed memory parallelism via MPI to parallelize over the atoms in the system, 2) On node, shared memory, parallelism is achieved for both parallelization over atoms as well as over energy points on the integration contour, 3) the calculation of the multiple scattering matrix uses GPU acceleration when available. An additional level of parallelism is provided by the capability to perform Wang-Landau Monte-Carlo sampling of magnetic and chemical order. This allows the first principles statistical physics calculation of magnetic and ordering phase transitions. By utilizing multiple Monte-Carlo walkers, the LSMS scalability is extended by multiple orders of magnitude.

It has traditionally exhibited near perfect scalability on massively parallel high performance computer architectures. It can exploit GPUs to accelerate the computations to enable first principles calculations of O(100,000) atoms and statistical physics sampling of finite temperature properties. Using the Cray XK7 system Titan at the Oak Ridge Leadership Computing Facility the LSMS code has demonstrated a sustained performance of 14.5PFlop/s and a speedup of 8.6 compared to the CPU-only code.