The initial condition

When conducting simulations it is often convenient to use the end result of one simulation as the initial condition to a new simulation. However, sometimes you need to generate a fresh initial condition. This can be done from a terminal window by executing the commands given below.

First make a directory where you want your first simulation to be performed. Call it e.g. ~/Test/, and go to that directory:

mkdir Test
cd Test

Next, run the rumd_init_conf program (make sure RUMD_home/Tools/ is in your path):

rumd_init_conf --lattice=fcc --cells=6

This command produces a file called start.xyz.gz that we will use as the initial configuration. The flag --lattice=fcc tells the program to generate a fcc crystal, and the flag --cells=6 that is should make six unit cells in each direction. The fcc lattice have four particles in the unit cell, and the final configuration will have $4\times6^3=864$ particles. We have not specified a density or temperature to the program, and it will use default values of $\rho=1.0$ and $T=1.0$, respectively. Note that rumd_init_conf have many options for generating configurations. A summary of these can be seen by typing

 
rumd_init_conf --help

rumd_init_conf also accept “short arguments” and the command to generating the fcc lattice simply done with

rumd_init_conf -lfcc -c6