[QE-developers] Laue-RISM screening (qe-rism-6.5.0)

[Kaňka Jiří]

Dear QE-ESM-RISM developers,

What are the relations between the room in an expand-cell available for solvent ions and the solution ionic strength?
Should it be always set in such way that there is a sufficient number of counterions for a full screening of the solute charge?

The first case below meets the requirement for neutrality: solute charge = - solvent charge, the second case does not meet the neutrality condition,
despite this the Laue-Rism calculation converged. If the calculation is still correct, it would enable me to investigate the screening of
charged carboxyl groups vs solvent ionic strength and the image of the unscreened charge on the electrode surface charge distribution.
Is it possible within the qe-esm-rism program to prevent the screening of the charged molecule which coerresponds to a real situation
when a solution with a low ionic-strength is used and in the solution there are only dissociated counter ions and the ions setting a required pH?

solute: Au(111)+ Alkanethiol (3MPA)SAM with deprotonated end carboxyl groups (COO-), 4 SAM molecules within a unit supercell (2*sqrt(3}x2*sqrt(3))R30

solute total charge -4


solvent: H2O+NaCl(aq)

1M Na+ 1M Cl-


End of Laue-RISM calculation


     convergence has been achieved in   563 iterations


     solvent charge    4.00115, renormalised to    4.00000

     Total number of solvent (in expand-cell)
     H2O          195.025857
     Na+            7.303247
     Cl-            3.303196

     Total charge of solvent (in expand-cell)
     H2O            0.001091 e
     Na+            7.303247 e
     Cl-           -3.303196 e
     Total          4.001141 e

     Chemical potential of solvation (in expand-cell)
     H2O        GaussFluct  -0.155709E+03 kcal/mol
     Na+        GaussFluct   0.119601E+05 kcal/mol
     Cl-        GaussFluct  -0.115505E+05 kcal/mol
     Total      GaussFluct   0.253883E+03 kcal/mol


0.1M Na+ 0.1M Cl-

End of Laue-RISM calculation


     convergence has been achieved in   185 iterations


     solvent charge    0.00030, renormalised to    0.00000

     Total number of solvent (in expand-cell)
     H2O          193.416542
     Na+            0.344344
     Cl-            0.344147

     Total charge of solvent (in expand-cell)
     H2O            0.000101 e
     Na+            0.344344 e
     Cl-           -0.344147 e
     Total          0.000297 e

     Chemical potential of solvation (in expand-cell)
     H2O        GaussFluct   0.119841E+03 kcal/mol
     Na+        GaussFluct  -0.427886E+01 kcal/mol
     Cl-        GaussFluct   0.475620E+01 kcal/mol
     Total      GaussFluct   0.120318E+03 kcal/mol


Thank you.

Best regards,

Jiri Kanka
Optical Biosensors dpt.
Institute of Photonics and Electronics
Czech Academy of Sciences
Prague
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/developers/attachments/20210417/aad09753/attachment.html>