4.2 Continuous Potentials

Considering the Lennard-Jones interaction, we find for the pair force

where .

The above-mentioned *nearest image convention* (NIC) is used in the
evaluation of the force acting on a particle.

Having determined this total force, the equation of motion
for particle may be numerically integrated.
A widely used technique is Verlet's algorithm

(with ).

Write a subroutine MOVE to integrate the equations of motion by a suitable
algorithm such as Verlet's. Having advanced each particle for one
time step, do not forget to apply *periodic boundary conditions*
to retain them all in the simulation box.

Write a main routine that puts the subroutines STARTCONF, ENERGY and MOVE to work. Test your first MD code by monitoring the mechanically conserved quantities.

Do a number of MD steps - say, - - and average the
quantity
to estimate the actual temperature.
To adjust the temperature to a desired value, scale all
velocity components of all particles in a suitable way. Repeat
this procedure up to 10 times. After - steps the
fluid will normally be well randomized in space, and the temperature
will be steady - though fluctuating slightly.

F. J. Vesely / University of Vienna