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Manuscript Title: Molecular dynamics simulation program of order N for condensed matter. I. MDPYRS1: scalar pyramid, short-range interactions.
Authors: Z.A. Rycerz, P.W.M. Jacobs
Program title: MDPYRS1
Catalogue identifier: ABRW_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 60(1990)53
Programming language: Fortran.
Computer: CYBER 180/S2-835, CYBER 930-31.
Operating system: NOS 2.6.1, NOS/VE 1.4.1.
RAM: 30K words
Word size: 64
Peripherals: disc.
Keywords: Solid state physics, Condensed matter, Simulation, Other, Molecular dynamics.
Classification: 7.7.

Nature of problem:
Study of the thermodynamic, structural and dynamic properties of liquids or solids.

Solution method:
A system of N mutually interacting particles is simulated. The classical equations of motion are solved at successive time steps, at each of which the force acting upon each particle, due to its interaction with the other particles contained in the sphere of cut-off radius Rc, is calculated. Periodic Boundary Conditions (PBC) are applied to the system in order to make it pseudo-infinite. When the system reaches thermal equilibrium, thermodymanic measurements are made by averaging over time. The basic quantities which are (or, optionally, can be) calculated directly in the program are: average temperature, potential energy, kinetic energy, total energy, virial, internal pressure, radial distribution function, mean square displacement, diffusion coefficient and 4th moment of dynamic structure factor. Data such as coordinates, velocities and forces at sucessive time steps are saved for further analysis.

Because both central computer memory and cpu time depend linearly on the number of particles, there are no special restrictions on the size of the simulated system. Depending on available computer memory and computer speed, N may change from about 10**2 to 10**5 (10**6) particles. In the present program the particles interact by central short-range forces.

Running time:
The over-all program speed expressed in number of interactions per cpu second is on the CDC 930 equal to ^ 23000 (or 44 musec/interaction) and remains almost constant for any Rc and N. Thus, the speed in number of particles per cpu sec [p/sec] is equal to 23000/AVNNN, where AVNNN= 4*phi/3 * rho R3c is the average number of nearest neighbours contained in the Rc sphere and rho ia a number density. Therefore in the case of liquid lead, where Rc = 5.7 Angstrom, the AVNNN = 29 and at Rc = 8.0 Angstrom, the AVNNN = 85, the speeds are equal to 750 [p/sec] and 270 [p/sec], respectively. As an example, the cpu time for a run of 1000 time steps with N = 1000 is equal to ca. 22 min (for Rc = 5.7 Angstrom). Both computers, namely the CDC 930 and CDC 835 have similar speeds.