From ef5b603e1d616e68c26dc217fcd4234e264f4afc Mon Sep 17 00:00:00 2001
From: Giovanni Bussi <giovanni.bussi@gmail.com>
Date: Wed, 18 Feb 2015 15:49:29 +0100
Subject: [PATCH] Added notice on need for WHOLEMOLECULE

---
 src/vatom/COM.cpp    | 5 +++++
 src/vatom/Center.cpp | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/src/vatom/COM.cpp b/src/vatom/COM.cpp
index 45323ef01..3edd46e15 100644
--- a/src/vatom/COM.cpp
+++ b/src/vatom/COM.cpp
@@ -39,6 +39,11 @@ an atom list through the label for the COM action that creates it.
 
 For arbitrary weights (e.g. geometric center) see \ref CENTER.
 
+When running with periodic boundary conditions, the user should take care 
+that the atoms in the COM group actually are in the proper periodic image.
+This is typically achieved using the \ref WHOLEMOLECULE action
+before COM calculation.
+
 \par Examples
 
 The following input instructs plumed to print the distance between the
diff --git a/src/vatom/Center.cpp b/src/vatom/Center.cpp
index e73d2f759..6915ff571 100644
--- a/src/vatom/Center.cpp
+++ b/src/vatom/Center.cpp
@@ -40,6 +40,11 @@ Notice that the generated virtual atom has charge equal to the sum of the
 charges and mass equal to the sum of the masses. If used with the MASS flag,
 then it provides a result identical to \ref COM.
 
+When running with periodic boundary conditions, the user should take care 
+that the atoms in the COM group actually are in the proper periodic image.
+This is typically achieved using the \ref WHOLEMOLECULE action
+before COM calculation.
+
 \par Examples
 
 \verbatim
-- 
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