Dear Nadjib Chafai,

Do you mean literally PURE HCl, without any water? Because what an experimentalist mean by HCl is hydrochloric acid, which is aqueous solution: for example, 37% HCl in H2O is "concentrated" hydrochloric acid. Then, the dielectric constant would be more like that for water (much higher than 5).

In that case you must specify the dielectric constant of the HCl, it must be around 5.

To do that in gaussian you have to write an input as for example:

# rb3lyp/6-311++g(d,p) scrf=Read

at the end of the .gjf file add:

eps = 5

and add a blank line as usual

Exaple:

# rb3lyp/6-311++g(d,p) scrf=Read

Title Card Required

0 1

C 0.00000000 0.00000000 0.00000000

H 0.00000000 0.00000000 1.07000000

H 1.00880579 0.00000000 -0.35666635

H -0.50440312 -0.87365131 -0.35666635

H -0.50440269 0.87365135 -0.35666686

eps=5

Dear Nadjib Chafai,

Do you mean literally PURE HCl, without any water? Because what an experimentalist mean by HCl is hydrochloric acid, which is aqueous solution: for example, 37% HCl in H2O is "concentrated" hydrochloric acid. Then, the dielectric constant would be more like that for water (much higher than 5).

I agree with Dr. Basiuk. You should use solvent mixture not only HCl. You may look for scrf=(iefpcm,solvent=generic,read) option where other than dielectric constant some other properties need to define.

How about using water as implicit solvent while some HCl molecules included in the calculation explicitly for such situations? (Requesting comments from Dr. Debashish and Dr. Nashik)

"Dr. Basuik" not "Dr.Nashik"

Extremely sorry for the spelling mistake

Dr. Patil use of explicit solvent is useful but the computation is very tricky. There are so many things need to take care e.g., No of HCl molecules their self-interactions and interaction with solute etc.

Thanks for clarifying...

Dear colleagues,

Thank you very much for the help.

Regards

Dr. Nadjib Chafai

As a brief note... HCl is a strong acid. Simulating HCl with a polarizable continuum may be extremely inaccurat, as it is very likely that HCl will react or interact in some specific way with the solute. Check whether your simulation makes sense... you may need explicit solvation.

Dear Mr. Rubén Laplaza, Thank you very much for the help. Regards Dr. Nadjib Chafai