Hello all,

It is given in manula that by default Lammps takes units in lj system.

So in my simulation i gave mass and lj potentials as following:

mass * 1.0

pair_style lj/cut 2.5

pair_coeff * * 1.0 1.0 2.5

Now can some one help me out in converting the output length and time scales.

By what factor I’ve to multiply to get the length in metres and time in seconds.

Thank you.

The length scale depends on what density

you chose for the lattice, via the lattice command.

See its doc page.

A text book on MD will explain unitless LJ vs other

units. E.g. see Allen & Tildesley. They have an appendix

on it.

Steve

Here’s my lattice command

lattice hex 0.93

take a look at the definition of reduced lj units. the book that steve mentions or the lammps manual should be enough to convert from the units you have to meters

Still under confusion…this terminology is not so familiar for me. Checked the reference too…can some one with patience help me out please?

lattice hex 0.93

mass * 1.0

pair_style lj/cut 2.5

pair_coeff * * 1.0 1.0 2.5

These are all enough for the conversion factors, right?

Still under confusion..this terminology is not so familiar for me. Checked

the reference too..can some one with patience help me out please?

read a text book that explains reduced units. nothing we can tell you here

will beat that. all we can do is give you a stripped down version of it.

i have silly question, though. why on earth do you use reduced units, if

you need to use "real" units afterwards. why not start with "real" right

away?

axel.