high binding energy

[Matt W]

Hi Sandeep,

there is nothing very obviously wrong with your input.

Maybe the basis set is not good enough for the anion? You could see whether 
extra diffuse functions make a big difference...

Matt

On Tuesday, July 3, 2012 11:13:18 AM UTC+1, sandeep wrote:
>
> Hi,
>     Towards solving this, I have done binding energy calculations for 
> molecular systems (where they interact through hydrogen bonds) and this 
> value matches with MP2 results. 
>
> It looks like the problem comes in for ionic systems. Did i missed any 
> keyword in my input file ?
>
> Hope this helps somebody to comment on my input file ...
>
> Thanks & Regards,
> Sandeep
>
>
>
> On Mon, Jul 2, 2012 at 6:31 PM, Sandeep Kumar Reddy <kuma... at gmail.com>wrote:
>
>> Dear all,  
>>              I want to calculate binding energy and compare with 
>> Gaussian's result and then i would like to proceed to bulk simulations.
>>
>> My system one ion pair (it's an ionic liquid). I did geometry 
>> optimizations of cation, anion and ion-pair and calculated the binding 
>> energy. This value is equal to  *-119* *kcal/mol*. After adding BSSE 
>> corrections, it is reduced to *-116* kcal/mol. For comparison, i carried 
>> out same calculations at MP2/aug-cc-pVDZ level using Gaussian package and 
>> this value is equal to -104 kcal/mol (BSSE corrected). A difference of 10 
>> kcal/mol of such calculation is discouraging. 
>>
>> (I have used same functional, cell parameters, cutoff, potentials for all 
>> three calculations)
>>
>>
>> I repeated the calculations by changing cutoff (to 480 Ry) and increasing 
>> box length (20 \AA). But it gives me same binding energy. Additionally, i 
>> have done same calculations in plane wave basis set using CPMD code. It 
>> gives 105 kcal/mol, very close to MP2 result. 
>>
>> I am not able to figure out why it happens.  Could anybody comment on my 
>> input files ?
>>
>>
>> *Ion-pair :*
>>
>> &GLOBAL
>>   PROJECT dimethyl_ammonium_bromide
>>   RUN_TYPE GEO_OPT
>>   PRINT_LEVEL MEDIUM
>> &END GLOBAL
>>
>> &FORCE_EVAL
>>   METHOD Quickstep
>>   &DFT
>>     BASIS_SET_FILE_NAME  /panfs/home/Xsreddy/cp2k/tests/QS/BASIS_MOLOPT
>>     POTENTIAL_FILE_NAME  /panfs/home/Xsreddy/cp2k/tests/QS/POTENTIAL
>>     &MGRID
>>       CUTOFF 280
>>       NGRIDS 5
>>     &END MGRID
>>     &QS
>>       METHOD       GPW    
>>       EPS_DEFAULT  1.0E-10 
>>     &END QS 
>>     &SCF
>>       MAX_SCF   50
>>       EPS_SCF   1.0E-6
>>       SCF_GUESS ATOMIC
>>       &OT ON
>>         MINIMIZER       CG
>>         PRECONDITIONER  FULL_ALL
>>         ENERGY_GAP      0.001
>>       &END OT
>>       &OUTER_SCF
>>         MAX_SCF  100
>>         EPS_SCF  1.0E-6  
>>       &END OUTER_SCF
>>     &END SCF
>>     &XC
>>       &XC_FUNCTIONAL  BLYP
>>       &END XC_FUNCTIONAL
>>       &vdW_POTENTIAL
>>         DISPERSION_FUNCTIONAL PAIR_POTENTIAL
>>         &PAIR_POTENTIAL
>>           TYPE DFTD2
>>           REFERENCE_FUNCTIONAL BLYP 
>>         &END PAIR_POTENTIAL
>>       &END vdW_POTENTIAL
>>     &END XC
>>     &POISSON
>>      POISSON_SOLVER WAVELET
>>      PERIODIC NONE
>>     &END POISSON
>>   &END DFT
>>   &SUBSYS
>>     &CELL
>>       ABC 20.0 20.0 20.0
>>       PERIODIC NONE
>>     &END CELL
>>     &COORD
>>     H       1.82622900    0.00011700    1.45609900
>>     H       0.41368700   -0.00011700    0.43855600
>>     N       1.53927100    0.00002300    0.47861600
>>     C       1.97625500   -1.24136700   -0.20041700
>>     H       3.06445100   -1.28419200   -0.25417500 
>>     H       1.58040100   -2.09266400    0.34985900 
>>     H       1.53907000   -1.23367800   -1.19754500 
>>     C       1.97589400    1.24149000   -0.20039300 
>>     H       1.54099200    1.23242900   -1.19850300 
>>     H       1.57755100    2.09264100    0.34831700 
>>     H       3.06414500    1.28582600   -0.25177600 
>>     Br     -1.40269500   -0.00003600   -0.01818000 
>>     &END COORD
>>     &TOPOLOGY
>>       &CENTER_COORDINATES
>>       &END
>>     &END 
>>     &KIND H   
>>       BASIS_SET  DZVP-MOLOPT-GTH
>>       POTENTIAL  GTH-BLYP-q1
>>     &END KIND 
>>     &KIND C
>>       BASIS_SET  DZVP-MOLOPT-GTH
>>       POTENTIAL  GTH-BLYP-q4
>>     &END KIND 
>>     &KIND N
>>       BASIS_SET  DZVP-MOLOPT-GTH
>>       POTENTIAL  GTH-BLYP-q5
>>     &END KIND 
>>     &KIND Br
>>       BASIS_SET  DZVP-MOLOPT-SR-GTH
>>       POTENTIAL  GTH-BLYP-q7 
>>     &END KIND 
>>   &END SUBSYS
>> &END FORCE_EVAL
>> &MOTION
>>   &GEO_OPT
>>     MAX_FORCE 0.0001
>>     MAX_ITER 500
>>     OPTIMIZER BFGS
>>   &END GEO_OPT
>> &END MOTION 
>>
>>
>> Other input files are enclosed. 
>>
>> Thanks.
>>
>> Regards,
>>  Sandeep
>>
>>
>> *
>> *
>>
>>
>>
>>
>>
>>
>
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