[CP2K:4719] dbcsr error when applying periodic efield

David Stelter base... at gmail.com
Thu Nov 7 19:02:23 CET 2013


Hi Matt,

Sorry  for the long delay, I realized there was also a problem with SCF 
with the test runs. I have fixed that as well. There still seems to be 
several energy discrepancies between the various methods of applying a 
external potential/electric field. I've also included output results for 
all runs with fixed SCF, both for orgin-centered and non-centered water 
molecules.
The energies are as follows.

*For an off-origin water molecule:*
NO FIELD
  -17.109346858835565

PERIODIC_EFIELD
  -17.087299531020836

EXTERNAL_POTENTIAL (FORCE_EVAL ONLY)
  -17.098300834804430

EXTERNAL_POTENTIAL (DFT ONLY)
  -17.128494982693702

EXTERNAL_POTENTIAL (FORCE_EVAL AND DFT)
  -17.102033317272440

It seems as if EXTERNAL_POTENTIAL (DFT) is stabilizing the molecule while 
the PERIODIC_EFIELD destabilizes the energy. All sections are applying a 
field to the water molecule in the same direction with identical strength. 
Any thoughts why this is happening? Shouldn't they have the same effect?

*For an origin-centered water molecule:*
NO FIELD
  -17.109567168504295

PERIODIC_EFIELD
  -17.109580046528809

EXTERNAL_POTENTIAL (FORCE_EVAL ONLY)
  -17.109567168504295

EXTERNAL_POTENTIAL (DFT ONLY)
  -17.518285260351075

EXTERNAL_POTENTIAL (FORCE_EVAL AND DFT)
  -17.189053596811391

Any input would be great!


Thanks,
David

On Wednesday, October 30, 2013 1:50:55 PM UTC-4, Matt W wrote:
>
> Before going any further - the external potential undergoes a large!!! 
> jump at the cell boundary - AxY - so with your water molecule straddling 
> the origin of the cell strange things may be happening. 
>
> Advantage to periodic field.
>
> Center the molecule in the cell and see if the differences are so bad. I 
> could reproduce polarizability (H2O molecule) and dielectric constants 
> (Si/SiO2 slab) for non periodic systems by applying the field, so am pretty 
> convinced the external potential works there.
>
> Matt
>
> On Wednesday, 30 October 2013 14:38:51 UTC, David Stelter wrote:
>>
>> Hi Matt and Flo,
>>
>> There seem to be some descrepencies in the methods mentioned above. I've 
>> done a few tests on a single water molecule with multiple versions of 
>> EXTERNAL_POTENTIAL and PERIODIC_EFIELD as well as no efield.
>>
>> The energies I obtained for a single water for various inputs are as 
>> follows with an inputted/ideal e-field strength of 0.1 V/angstrom
>> 1) no field, E =   -15.902943301939017
>>
>> 2) PERIODIC_EFIELD, E =   -15.901968922615296
>>
>> 3) EXTERNAL_POTENTIAL in the FORCE_EVAL section only, E =   
>>  -15.90294330193902
>>
>> 4) EXTERNAL_POTENTIAL in the DFT section only, E =   -16.227568014660498
>>
>> 5) EXTERNAL_POTENTIAL in both sections, E =   -15.971096979028731
>>
>> It seems there is another section of EXTERNAL_POTENTIAL that works under 
>> the FORCE_EVAL section rather than DFT. At first inspection, it seems that 
>> this section would only apply to the MM region of the cell as there is 
>> basically no difference between values 1 and 3. However, as you can see, 
>> there is a large difference between 4 and 5 where EXTERNAL_POTENTIAL is 
>> applied to both the DFT and FORCE_EVAL sections.
>>
>> Additionally, it should be noted that PERIODIC_EFIELD is being used with 
>> a value of 20x10^-4 au in the Y direction, which corresponds to 
>> ~0.1V/angstrom while EXTERNAL_POTENTIAL is being used via the function 
>> Y*(A/B) with values of 0.1 [eV] and 1 [angstrom] as suggested by Matt to 
>> obtain a 0.1V/angstrom field. However, as you can clearly see, the energy 
>> values are VERY different which leads me to believe there is something 
>> wrong! I am not using ROKS or QM/MM for this sim thus PERIODIC_EFIELD 
>> should work fine; additionally the manual is very clear and explicit by 
>> saying the input is in au. This makes me fairly confident in the accuracy 
>> of this calculation for the energy of 1 QM water in a 0.1V/angstrom field
>>
>> I am still unsure regarding the units of EXTERNAL_POTENTIAL. eV/Angstrom 
>> is a force, multiplied by Z, a unit length, brings us back to an energy of 
>> 0.1 eV which is being applied to the system. I guess I am confused 
>> regarding Matt's calculation of efield strength from 0.1 eV/Angstrom input. 
>> Any light that can be shed on how the EXTERNAL_POTENTIAL process works and 
>> how the potential is being applied would be great as I am certain that the 
>> input for EXTERNAL_POTENTIAL is resulting in a field strength much higher 
>> than 0.1 V/angstrom. 
>>
>> I've attached my input/output files of the sims. It should also be noted 
>> that these input files came from the test folder of cp2k and are identical 
>> except for the various electric field codes.
>>
>> Thanks,
>> David
>>
>> On Monday, October 28, 2013 9:18:29 AM UTC-4, Matt W wrote:
>>>
>>> Hi David,
>>>
>>> On Friday, October 25, 2013 9:03:09 PM UTC+1, David Stelter wrote:
>>>>
>>>> Hi Matt,
>>>>
>>>> We have looked into EXTERNAL_POTENTIAL, some guidance on the section 
>>>> would be appreciated! I've read on these forums that people have put an 
>>>> efield value as a parameter in this section. How is this section treated? I 
>>>> want to apply an efield, but shouldn't I be putting in a potential 
>>>> multiplied by some distance of the periodic box?
>>>>
>>>>
>>> in the DFT section
>>>
>>> &EXTERNAL_POTENTIAL
>>>     FUNCTION Z*(A/B)
>>>     PARAMETERS A B
>>>     VALUES [eV] 0.1 [angstrom] 1.0
>>> &END
>>>
>>> should add a field of 0.1 V/A along the Z direction of your QM cell. 
>>> This is just a classic sawtooth potential - but as your QM region has 
>>> vacuum around it there should be no issues.
>>>
>>> As Flo notes for the periodic_efield, I think this will only act on the 
>>> QM region. Adding a similar potential over the classical region would cause 
>>> issues with periodicity. 
>>>
>>> I haven't tried it in combination with ROKS or QMMM.
>>>
>>> Maybe an easier solution is just to add some artificial charges into the 
>>> MM region to generate the field? Though you'd have to take into account 
>>> that their effect would get screened by solvent...
>>>
>>> Matt
>>>
>>>
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