[Pw_forum] How to calculate Mean Square Displacement (MSD)

[Lorenzo Paulatto]

On 30/10/17 08:29, Nam Tran wrote:
> I do not know whether I should consider the distance with atom that goes 
> about outside the box (a) or its image (b). Please check the image below 

Usually the right thing is to consider the smallest of all the possible 
distances. I.e. you put the red atom in all the positions which are 
equivalent by periodic boundary conditions, these in principle are 
infinite but going up to the second neighboring cell is usually more 
than enough; for each case you take the distance with the blue atom, and 
you take the minimum of all the distances.

kind regards


-- 
Lorenzo Paulatto - Paris