about scaled coordinate.

Hello, LAMMPS users.

I have a question about scaled coordinate on LAMMPS dump (style atom) command.

Is scaled coordinate value on triclinic system (when tilt-factor is not 0.) following actual box geometry vectors

(geometry vectors : linearly independent set of vectors)

or just the scaled value of a box length along whatever-coordinate(typical x and y, z)?

I am not good at cpp language to look out a detail of a source code. :frowning:

pre-thanks for your future help!

Jo You-Hwan
[email protected]

Here’s what the dump doc page says:

There are several options for outputting atom coordinates. The x, y, z attributes write atom coordinates “unscaled”, in the appropriate distance units (Angstroms, sigma, etc). Use xs, ys, zs if you want the coordinates “scaled” to the box size, so that each value is 0.0 to 1.0. If the simulation box is triclinic (tilted), then all atom coords will still be between 0.0 and 1.0. Use xu, yu, zu if you want the coordinates “unwrapped” by the image flags for each atom. Unwrapped means that if the atom has passed thru a periodic boundary one or more times, the value is printed for what the coordinate would be if it had not been wrapped back into the periodic box. Note that using xu, yu, zu means that the coordinate values may be far outside the box bounds printed with the snapshot. Using xsu, ysu, zsu is similar to using xu, yu, zu, except that the unwrapped coordinates are scaled by the box size. Atoms that have passed through a periodic boundary will have the corresponding cooordinate increased or decreased by 1.0.

So each x,y,z coord for triclnic is the fraction along the box geometry vector,

i.e. a coefficienct on the set of (non-orthogonal) tricilinc basis vectors that describe the simulation box.