[gmx-users] Mixture of H2O and D2O

Hernan Ahumada hernan at chem.gla.ac.uk
Tue Jan 10 12:35:33 CET 2012

Dear gmx users

I am trying to run a MD with a mixture of D2O and H2O. I defined a new itp
spcdeut.itp for heavy water and the usualy spc.itp for normal water. when I try
to run grompp appear this error:

"The [molecules] section of your topology specifies more than one block of
a [moleculetype] with a [settles] block. Only one such is allowed. If you
are trying to partition your solvent into different *groups* (e.g. for
freezing, T-coupling, etc.) then you are using the wrong approach. Index
files specify groups. Otherwise, you may wish to change the least-used
block of molecules with SETTLE constraints into 3 normal constraints."

Any of you can help me with te meaning of this error? because if I define
=-DFLEXIBLE I solve the error.

Thank you very much

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