A question about the periodic boundary condition

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Hang LYU

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Jul 10, 2021, 10:00:10 PM7/10/21
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Dear developers and users,
   I am now not very clear of the periodic boundary condition in plumed. For example, I am using the COORDINATION function of plumed to calculate the cordination number of atom A. In the periodic simulation box, r_AB is larger than the cut-off distance, however, when we consider the distance between atom A and the replica (B') of atom B in the neighboring box, r_AB' is smaller than the cut-off distance. My question is whether atom B will be considered inside the first coordinate sphere of atom A by plumed.

Regards,
Hang LYU
IMG_0131(20210711-094737).PNG

Giovanni Bussi

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Jul 11, 2021, 10:11:41 AM7/11/21
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Hi,

with or without cutoff, by default COORDINATION will use the distance with the closest image (r_AB' in your picture), unless you override this default behavior with NOPBC. Then, that distance might be compared with the cutoff D_MAX to know if it should be ignored

Giovanni


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Hang LYU

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Aug 3, 2021, 6:44:22 PM8/3/21
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Thank you very much
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