[gmx-users] query on table potential

2012-06-07 Thread Sanku M
Hi,
  I am trying to use a table potential implementing Weeks-Chandler-Anderson 
(WCA) interaction between a solute and all atoms of a solvent like TIP3P water 
( with nonzero interaction in the Hydrogen atoms) . But, I am having a trouble 
in specifying energy groups required for table potential. 
Here is the problem:
 I have two atom types in water : OW and HW. and one atom type in solute : POL

Now, I want to use  two Table potentials with WCA interactions between a) POL  
HW and b) POL  OW 
So, I created two table potential files: table_POL_HW.xvg and table_POL_OW.xvg

and then
in the .mdp file, I specified 
energygrps = POL OW HW 
energygrps_table = POL OW POL HW

But, compiling the .mdp file using grompp ( version 4.5.4)  gives me following 
error
Fatal error:                
atoms 33 and 34 in charge group 1 of molecule type 'SOL' are in different 
energy groups

Clearly, using OW and HW as separate energy groups is causing the problem.
So, I am looking for an option on how I can use the table potential between 
solute and each atoms of solvent.

Any help will be appreciated.
Sanku-- 
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Re: [gmx-users] query on table potential

2012-06-07 Thread Mark Abraham

On 8/06/2012 1:09 PM, Sanku M wrote:

Hi,
  I am trying to use a table potential implementing 
Weeks-Chandler-Anderson (WCA) interaction between a solute and all 
atoms of a solvent like TIP3P water ( with nonzero interaction in the 
Hydrogen atoms) . But, I am having a trouble in specifying energy 
groups required for table potential.

Here is the problem:
 I have two atom types in water : OW and HW. and one atom type in 
solute : POL


Now, I want to use  two Table potentials with WCA interactions between 
a) POL  HW and b) POL  OW
So, I created two table potential files: table_POL_HW.xvg and 
table_POL_OW.xvg


and then
in the .mdp file, I specified
energygrps = POL OW HW
energygrps_table = POL OW POL HW

But, compiling the .mdp file using grompp ( version 4.5.4)  gives me 
following error

Fatal error:
atoms 33 and 34 in charge group 1 of molecule type 'SOL' are in 
different energy groups


Clearly, using OW and HW as separate energy groups is causing the problem.
So, I am looking for an option on how I can use the table potential 
between solute and each atoms of solvent.




Energy groups can only be unions of complete charge groups. So your 
energy groups require that you split the solvent charge group. The 
solvent charge groups are defined in its [moleculetype]. Splitting will 
mean that you will get integration artefacts at the cut-off unless you 
use a proper long-ranged electrostatic method (i.e. an Ewald family method).


Mark
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