Dear lammps user,

My lammps version is 7 August 2019.

As far as I know the meaning of the random numbers in some lammps command such as velocity command is that they are used as seeds to generate random velocities.

Should I pay certain attention when choosing these numbers or can I set whatever number I want like 8, 438758, or 10000002 ?

Does the choice of these random numbers relate to the physics of the system being simulated by any means?

According to my understanding, sine these integer numbers are random, someone can choose any integer numbers appearing in their mind suddenly.

Much thanks in advance.

Best regards

Mohammed

Random number generators like the ones used by LAMMPS are not producing truly random numbers, but follow an algorithm that creates “pseudo random” numbers. there are different algorithms for that with different “quality”. all of them are deterministic, i.e. when started from a given state, they will generate the exact same sequence of pseudo random numbers. they all also have a “sequence length” after which they repeat the same sequence of pseudo random numbers.

the option to provide a seed gives you the opportunity to a) reproduce the exact same sequence of pseudo random numbers, when desired (very useful for debugging), and b) improve decorrelation, if you need to start multiple independent simulations starting from the same kind of geometry. when using different seeds, you have a better chance of exploring the available phase space and avoid unwanted correlations (and thus bogus results).

There should be plenty of discussion of this in text books about simulations that also cover monte carlo simulations.

Axel.