[gmx-users] maximum cut-off in Minimum image convention

[Francisco Garcia]

Dear users,

I wish to ask a question regarding the maximum cut-off in the minimum
image convention (MIC).

According to my understanding, MIC ensures that the separation
between two particles i and j along each coordinate axes, namely,
xi- xj, yi-yj, and zi-zj, is in the interval (-0.5L, 0.5L), where L is the box
length (assumed the box to be cubic). This implies that
distance rij can vary between 0 and 0.5L*sqrt(3).
In order words the maximum separation should be less than half the diagonal:
 for example if i is located at (0,0,0) and j is located at the corner
(0.49L, 0.49L, 0.49L).

However, I read a couple of text books and online notes that claim
that if r > 0.5L, then MIC is violated.
Specifically, this means that 0.5L < rij < 0.5L*sqrt(3)  violates MIC.
I find this confusing. I have been grinding hard to understand this
point but I just
cannot figure it out.

In short my claim is that in MIC, rij can be at most half the diagonal
length whereas
the textbook says that rij can be at most half the box length.

If I am wrong, can someone explain the flaw in my argument?

Thanks!