Writing a fix to apply the Andersen thermostat

Here is a list of changes made to the source code directory:

• These are the new files that have been created: fix_temp_andersen.cpp and fix_temp_andersen.h
• These are the existing files that have been modified: fix_temp_berendsen.cpp and fix_temp_berendsen.h.
• These are the methods that have been modified: constructor, and end_of_step()
• These are the input parameters: andFreq, seedMB, sigmaMB
• These are the other quantities introduced: random, me
• LAMMPS syntax: fix FIX_NAME GROUP temp/andersen FREQUENCY SEED SIGMA (we'll review this syntax later in this section)

In this section, we will write a fix to apply the Andersen thermostat that adjusts the temperature of particles by assigning random velocities to them at specified intervals.

Theory – Andersen thermostat

Based on the concept of velocity and momentum adjustments upon stochastic collisions in an atomistic system, the Andersen thermostat...