Hi, Laurent, I have checked it again, you are right. There is mistake
in the pressure tail.
Best wishes,
Chuanfu
On Tue, Jun 1, 2010 at 4:23 PM, Steve Plimpton <sjplimp@gmail.com> wrote:
> The force->numeric() version is better. I'll look at the tail
> correction for 96.
>
> Steve
>
> On Tue, Jun 1, 2010 at 6:54 AM, Laurent Joly <ljoly.ulyon@gmail.com> wrote:
>> Dear all,
>>
>> In order to implement a 30-6 Lennard-Jones pair potential (PRE 70,
>> 061507), I compared pair_lj_cut.cpp and pair_lj96_cut.cpp.
>>
>> * First I was wondering what was the difference between the two
>> methods to read the parameters:
>>
>>> cut_global = force->numeric(arg[0]);
>> --
>> < cut_global = atof(arg[0]);
>>
>> Is one of them better?
>>
>>
>> * Second I double checked and I really think there is a mistake in the
>> tail correction for pressure in the lj96/cut style:
>>
>> - For standard LJ it is:
>> < ptail_ij = 16.0*PI*all[0]*all[1]*epsilon[i][j] * sig6 * (2.0*sig6 -
>> 3.0*rc6) / (9.0*rc9);
>>
>> where the 1/r^6-related term is: (16/3) pi rho^2 epsilon sigma^6 / rc^3.
>>
>> For a 9-6 LJ pair potential it should be:
>>
>> 8 pi rho^2 epsilon sigma^6 (3sigma^3 - 4rc^3) / 6rc^6
>>
>> with the same 1/r^6-related term, but it is:
>>
>>> ptail_ij = 8.0*PI*all[0]*all[1]*epsilon[i][j] * sig6 * (3.0*sig3 - 2.0*rc3) / (6.0*rc6);
>>
>> So I would say the 2.0 before rc3 should be a 4.0... Do you confirm?
>>
>> Best regards,
>> Laurent
>>
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>>
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>
--
Best wishes,
Sincerely
Chuanfu Luo
Leibniz-Institute of Polymer Research Dresden
Hohe Str. 6
D-01069 Dresden, Germany
Tel.: +49 351 4658 744
Fax : +49 351 4658 752
email: luochuanfu@gmail.com; luo@ipfdd.de