Scaling forces per-atom

[Vivienne Pelletier]

Hi yall, 
I would like to perform a thermodynamic integration from one ff to another only for a specific atom in solution. Is there any simple way of doing this?

Thanks,

Vivienne

[Michele Ceriotti]

Yes, should be easy. You'll have two forcefields defined in the input, e.g.
  <ffsocket mode='unix' name='pot1'>
    <address> socket1 </address>
  </ffsocket>
  <ffsocket mode='unix' name='pot2'>
    <address> socket2 </address>
  </ffsocket>
and in the <system> block you add forces with the appropriate weights for each slice, e.g.
    <forces>
      <force forcefield='pot1' weight="0.1"/>
      <force forcefield='pot2' weight="0.9"/>
    </forces>
then if you need to print out the value of potentials to compute the averages and then the thermodynamic force for the integration

you can just use pot_component_raw(0) and pot_component_raw(1) in a <properties> output block.

Michele