Scientific Applications and Performance Tuning
UITS - Research Technologies
The IU-MD code performs molecular dynamics simulations of dense nuclear matter such as occurs in Type II supernovas, the outer layers of neutron stars, and in white dwarf stars. In less dense regions of these stellar objects, matter exists in a completely ionized state, where atomic nuclei still retain their identities, but have been stripped of all electrons. The electrons form a roughly uniform background Fermi gas. The IU-MD code simulates fully ionized atoms via a classical screened Coulomb interaction. An exponential screening factor models the screening effect of the background electron gas. These simulations have been used to study a number of properties of dense matter in compact stellar objects, such as chemical and phase separation, thermal conductivity, phase diagrams, and mechanical properties. Results can be compared with observational data to test theoretical models of matter under extremes of temperature, pressure and density. The benchmark performs a short run of a realistic 27648 ion system consisting of carbon and oxygen ions. Such matter exists in the outer layers of white dwarf stars.
The program requires an input parameter file named 'runmd.in' containing various parameters describing the MD simulation, such as initial particle configuration, number of time steps to run, temperature, how often to measure potential energy, interaction parameters, etc. It also requires a file called 'md.in' containing the initial configuration, i.e., all particle positions and velocities. This is a Fortran unformatted file whose first record is a real*8 timestamp, and whose second record is x,y,z, vx,vy,vz for all particles.
The data set uses two species with 22784 and 4864 ions.
The program outputs a final MD configuration as an unformatted Fortran file whose structure is the same as the input configuration file: a timestamp followed by x,y,z,vx,vy,vz for all particles. It also writes information about the progress of the run to standard out, and to a log file. The information includes run parameters from the runmd.in file, and periodic measurements of the potential, kinetic and total energy of the system.
C. J. Horowitz, D. K. Berry, E. F. Brown, Phase separation in the crust of accreting neutron stars Phys. Rev. E 75, 066101 (2007) DOI