About

XMD is a computer program for performing molecular dynamics simulations. It is designed for the simulation of metals and ceramics. It has the following features.

Computer System

• C source code is availble for easy porting to a variety of computers.
• Can be compiled using POSIX thread functions to take advantage of multi-CPU computers.

Molecular Dynamics

• Constant temperature using velocity re-scaling algorithm (CLAMP command).
• Constant pressure using either Andersen's algorithm or a simple volume "rescaling" algorithm suitable for lattice constant versus temperature calculations. (PRESSURE command).
• Efficient system relaxation (local minima) algorithm (QUENCH command).
• Constrain selected atoms to remain fixed in space (FIX command).
• Constrain selected atoms to remain in a line or plane (CONSTRAIN command).
• Apply an unique external force to individual atoms (EXTFORCE command).
• Tether selected atoms to their initial positions with springs of various spring constants (EXTSPRING command).
• Apply velocity damping coefficients to selected atoms (DAMP command).
• Uses pair potential, Embedded Atom Method potentials (EAM), Tersoff's Silicon-Carbide potential or Stillinger-Weber Si potential.

Program Input

• All program actions are controlled by commands read from one or more text files.
• A macro processor lets you enter strings from the command line or define strings within the command file (MACRO command).
• A built-in calculator with variables that can be used with all number input (CALC command).
• Input file instruct the reading of another input file (READ command).
• Flexible creation (FILL command) and editing of atomic structures.
• Select subsets of atoms using a variety of patterns (SELECT, SET and TAG commands).
• Perform actions on selected atoms, such as moving them (MOVE), inserting defects (SCREW, WAVE), setting atom type (TYPE), setting atom mass (MASS), rotating selected atoms (ROTATE), etc.
• Some commands (MOVE, DAMP, EXTFORCE and EXTSPRING) allow input values to be a function of atomic coordinates.

Program Output

• Save the complete simulation state for later continuation (WRITE STATE command).
• Accumulate system energies (ESAVE and WRITE ENERGY commands), atomic stress (SSAVE and WRITE STRESS commands), atom coordinates (WRITE PARTICLE command) and other information to text files during simulation.
• Coordinates can be stored in special compact format (RCV or COR commands) for later use with companion programs such as WMOVIEC which produces movies.
• Save atomic coordinates in a Protein Data Bank file for use with display software such as MSI's Cerius2 (WRITE PDB command), or standard XYZ format (WRITE XYZ command).
• Built-in plotting routines for plotting atom configuration in color on a Postscript device (PLOT command).