Dear all, <div> I want to calculate binding energy and compare with Gaussian's result and then i would like to proceed to bulk simulations.</div><div><br></div><div>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 <b>-119</b> <b>kcal/mol</b>. After adding BSSE corrections, it is reduced to <b>-116</b> 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. </div>
<div><br></div><div>(I have used same functional, cell parameters, cutoff, potentials for all three calculations)</div><div><br></div><div><br></div><div>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. </div>
<div><br></div><div>I am not able to figure out why it happens. Could anybody comment on my input files ?</div><div><br></div><div><br></div><div><b>Ion-pair :</b></div><div><br></div><div><div>&GLOBAL</div><div> PROJECT dimethyl_ammonium_bromide</div>
<div> RUN_TYPE GEO_OPT</div><div> PRINT_LEVEL MEDIUM</div><div>&END GLOBAL</div><div><br></div><div>&FORCE_EVAL</div><div> METHOD Quickstep</div><div> &DFT</div><div> BASIS_SET_FILE_NAME /panfs/home/Xsreddy/cp2k/tests/QS/BASIS_MOLOPT</div>
<div> POTENTIAL_FILE_NAME /panfs/home/Xsreddy/cp2k/tests/QS/POTENTIAL</div><div> &MGRID</div><div> CUTOFF 280</div><div> NGRIDS 5</div><div> &END MGRID</div><div> &QS</div><div> METHOD GPW </div>
<div> EPS_DEFAULT 1.0E-10 </div><div> &END QS </div><div> &SCF</div><div> MAX_SCF 50</div><div> EPS_SCF 1.0E-6</div><div> SCF_GUESS ATOMIC</div><div> &OT ON</div><div> MINIMIZER CG</div>
<div> PRECONDITIONER FULL_ALL</div><div> ENERGY_GAP 0.001</div><div> &END OT</div><div> &OUTER_SCF</div><div> MAX_SCF 100</div><div> EPS_SCF 1.0E-6 </div><div> &END OUTER_SCF</div>
<div> &END SCF</div><div> &XC</div><div> &XC_FUNCTIONAL BLYP</div><div> &END XC_FUNCTIONAL</div><div> &vdW_POTENTIAL</div><div> DISPERSION_FUNCTIONAL PAIR_POTENTIAL</div><div>
&PAIR_POTENTIAL</div><div> TYPE DFTD2</div><div> REFERENCE_FUNCTIONAL BLYP </div><div> &END PAIR_POTENTIAL</div><div> &END vdW_POTENTIAL</div><div> &END XC</div><div>
&POISSON</div><div> POISSON_SOLVER WAVELET</div><div> PERIODIC NONE</div><div> &END POISSON</div><div> &END DFT</div><div> &SUBSYS</div><div> &CELL</div><div> ABC 20.0 20.0 20.0</div>
<div> PERIODIC NONE</div><div> &END CELL</div><div> &COORD</div><div> H 1.82622900 0.00011700 1.45609900</div><div> H 0.41368700 -0.00011700 0.43855600</div><div> N 1.53927100 0.00002300 0.47861600</div>
<div> C 1.97625500 -1.24136700 -0.20041700</div><div> H 3.06445100 -1.28419200 -0.25417500 </div><div> H 1.58040100 -2.09266400 0.34985900 </div><div> H 1.53907000 -1.23367800 -1.19754500 </div>
<div> C 1.97589400 1.24149000 -0.20039300 </div><div> H 1.54099200 1.23242900 -1.19850300 </div><div> H 1.57755100 2.09264100 0.34831700 </div><div> H 3.06414500 1.28582600 -0.25177600 </div>
<div> Br -1.40269500 -0.00003600 -0.01818000 </div><div> &END COORD</div><div> &TOPOLOGY</div><div> &CENTER_COORDINATES</div><div> &END</div><div> &END </div><div> &KIND H </div>
<div> BASIS_SET DZVP-MOLOPT-GTH</div><div> POTENTIAL GTH-BLYP-q1</div><div> &END KIND </div><div> &KIND C</div><div> BASIS_SET DZVP-MOLOPT-GTH</div><div> POTENTIAL GTH-BLYP-q4</div><div>
&END KIND </div><div> &KIND N</div><div> BASIS_SET DZVP-MOLOPT-GTH</div><div> POTENTIAL GTH-BLYP-q5</div><div> &END KIND </div><div> &KIND Br</div><div> BASIS_SET DZVP-MOLOPT-SR-GTH</div>
<div> POTENTIAL GTH-BLYP-q7 </div><div> &END KIND </div><div> &END SUBSYS</div><div>&END FORCE_EVAL</div><div>&MOTION</div><div> &GEO_OPT</div><div> MAX_FORCE 0.0001</div><div> MAX_ITER 500</div>
<div> OPTIMIZER BFGS</div><div> &END GEO_OPT</div><div>&END MOTION </div><div><br></div></div><div><br></div><div>Other input files are enclosed. </div><div><br></div><div>Thanks.</div><div><br>Regards,</div><div>
Sandeep</div><div><br></div><div><br></div><div><b><br></b></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div>