## How do you define a group in Lammps?

Description. Identify a collection of atoms as belonging to a group. The group ID can then be used in other commands such as fix, compute, dump, or velocity to act on those atoms together. If the group ID already exists, the group command adds the specified atoms to the group.

## How do you calculate Lammps force?

Syntax

- ID, group-ID are documented in compute command.
- style = force/tally or heat/flux/tally or heat/flux/virial/tally or pe/tally or pe/mol/tally or stress/tally.
- group2-ID = group ID of second (or same) group.

**What is fix in Lammps?**

In LAMMPS, a “fix” is any operation that is applied to the system during timestepping or minimization. Examples include updating of atom positions and velocities due to time integration, controlling temperature, applying constraint forces to atoms, enforcing boundary conditions, computing diagnostics, etc.

### How do I restart Lammps?

You can use the write_restart command to write a restart file before a run begins. A restart file is not written on the last timestep of a run unless it is a multiple of N. A restart file is written on the last timestep of a minimization if N > 0 and the minimization converges.

### How is MSD calculated in Lammps?

compute msd command

- ID, group-ID are documented in compute command.
- msd = style name of this compute command.
- zero or more keyword/value pairs may be appended.
- keyword = com or average com value = yes or no average value = yes or no.

**How do you calculate the energy of an atom?**

A simple expression for the energy of an electron in the hydrogen atom is:

- E=−13.6n2 where the energy is in electron volts.
- n is the principle quantum number.
- So for an electron in n=1 :
- E=−13.6eV.
- To convert to joules you can x this by 1.6×10−19.

## What is restart file in Lammps?

Restart files are written on timesteps that are a multiple of N but not on the first timestep of a run or minimization. You can use the write_restart command to write a restart file before a run begins. A restart file is not written on the last timestep of a run unless it is a multiple of N.

## How do you calculate MSD?

MSD is defined as MSD=average(r(t)-r(0))^2 where r(t) is the position of the particle at time t and r(0) is the initial position, so in a sense it is the distance traveled by the particle over time interval t.

**How do you calculate MSD diffusion coefficient?**

By using the relation in wiki’s link, you then plot the MSD divided by (2*n*t) as a function of time, where n is the dimension of your MSD and t is the time itself. That is the value for the diffusion coefficient in that moment.

### How much energy is in a electron?

If an electron is in the first energy level, it must have exactly -13.6 eV of energy….Energy Levels of Electrons.

Energy Level | Energy |
---|---|

5 | -.54 eV |