Strange behaviour by molecule in Electric field
pkmis... at gmail.com
Tue Nov 12 17:02:45 CET 2013
This is really a serious bug. Now the reason is clear to me for translating
the system in -ve direction of the field which i was trying to figure out
fundamentally from last more than 2 months. After recompiling the code with
this change, My system (Single Hydrogen atom in constant EF and single
water molecule in Gaussian Pulse both for non-periodic box) is
translationally invariant in presence of EF. This is really helpful.
Thank you so much
On Friday, 8 November 2013 19:14:32 UTC+1, Matt W wrote:
> You make a very good point! Now for your argument to hold your system
> needs to be translationally invariant. There are two reasons (at least) why
> it is not.
> (i) the EFIELD is non periodic (i.e. a saw tooth), so there is a huge
> field at the cell edge. You need to centre your molecule in the box.
> (ii) your CUTOFF is not truly sufficient if you really want to see the
> molecule stay centred - there's a post from Flo discussing this concerning
> vibrational analysis from a month or so ago, but this is a minor point.
> BUT, I think you have also identified a bug. According to me, there is an
> inconsistency between the way forces due to the field act on atoms cores
> and electrons.
> changing line 233 (or thereabouts) of efield_utils.F to
> i.e. changing the sign of the forces on the cores, seems to give good
> conservation of force in my quick tests (plus comments above). You'll have
> to recompile, of course.
> Let us know if this seems to work for you (it is possible that the force
> on the electrons rather than the core should be inverted, but at the moment
> they are both being pushed in the same direction).
> On Friday, 8 November 2013 09:10:51 UTC, Pankaj Mishra wrote:
>> As per my fundamental knowledge, polar molecule can rotate in electric
>> field, not translate. Being more precise, here i am talking about 1
>> molecule in non-periodic box. I didn't find any force to move in the field.
>> Even non-polar molecule and single atom (H and Ne) are also translating
>> in EF in CP2K. In the case of water cluster, the center of mass of whole
>> system is translating. I have not found such behavior in other package like
>> GAMESS .
>> This is a very serious issue for me. Please try to suggest something if i
>> am missing anything in my input.
>> Thank you
>> On Thursday, 7 November 2013 20:23:58 UTC+1, Matt W wrote:
>>> just wondering: why would you not expect a polar molecule to move in an
>>> electric field?
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