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

[Otani Minoru]

Dear Jiri,

The charge neutrality must be always satisfied. Since your tot_charge=-4, the total charge of solvent must be converged to +4. Thus 1M NaCl calculation is correct. But 0.1M NaCl case, the solvent charge is too small. You need to reconstruct the model. 

Generally, the thickness of the EDL become thick as you decrease the density of salt. So, probably you need to expand the unit cell along z-direction (not the expand cell). 

Best regards,
Minoru 

--------------------------------------------------------------------------------------------------------
Minoru Otani
Professor,
Center for Computational Sciences and Faculty of Pure and Applied Sciences, 
University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
TEL: +81-29-853-4273
FAX: +81-29-853-6406
E-mail: otani at ccs.tsukuba.ac.jp
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> On Apr 17, 2021, at 20:56, Kaňka Jiří <kanka at ufe.cz> wrote:
> 
> 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
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