[gmx-users] Using SPC/E water with the OPLS force field

[Justin Lemkul]

On 7/21/16 1:15 PM, Miguel Caro wrote:
> Hello everyone,
>
> I am trying to use SPC/E water with the OPLS force field (I took the
> OPLS itp file available from virtualchemistry.org). There is a number of
> OW and HW atoms available (list below). At the moment I have chosen
> opls_111 and opls_112, respectively. Is there any "standard" pair that
> should be used? If I understand it correctly, the partial charges will
> be overwritten by the molecule topology, but the LJ parameters will be
> taken from the OPLS topology, so should I expect big differences if I
> use, e.g. opls_116 and opls_117?
>

Yes, because opls_111 and opls_112 are for TIP3P water, while opls_116 and 
opls_117 are actually for SPC and SPC/E.  So if you're combining opls_111 and 
opls_112 with SPC/E charges, you're not actually simulating SPC/E, but some 
untested hybrid TIP3P-SPC/E form.

-Justin

> Thanks,
> Miguel
>
>     #ifdef HEAVY_H
>      opls_111   OW  8      9.95140    -0.834       A    3.15061e-01
>     6.36386e-01
>      opls_112   HW  1      4.03200     0.417       A    0.00000e+00
>     0.00000e+00
>      opls_113   OW  8      9.95140     0.000       A    3.15365e-01
>     6.48520e-01
>      opls_114   HW  1      4.03200     0.520       A    0.00000e+00
>     0.00000e+00
>      opls_115   MW  0      0.00000    -1.040       D    0.00000e+00
>     0.00000e+00
>      opls_116   OW  8      9.95140    -0.820       A    3.16557e-01
>     6.50194e-01
>      opls_117   HW  1      4.03200     0.410       A    0.00000e+00
>     0.00000e+00
>     #else
>      opls_111   OW  8     15.99940    -0.834       A    3.15061e-01
>     6.36386e-01
>      opls_112   HW  1      1.00800     0.417       A    0.00000e+00
>     0.00000e+00
>      opls_113   OW  8     15.99940     0.000       A    3.15365e-01
>     6.48520e-01
>      opls_114   HW  1      1.00800     0.520       A    0.00000e+00
>     0.00000e+00
>      opls_115   MW  0      0.00000    -1.040       D    0.00000e+00
>     0.00000e+00
>      opls_116   OW  8     15.99940    -0.820       A    3.16557e-01
>     6.50194e-01
>      opls_117   HW  1      1.00800     0.410       A    0.00000e+00
>     0.00000e+00
>     #endif
>      opls_118   OW  8     15.99940     0.000       A    3.12000e-01
>     6.69440e-01
>      opls_119   HW  1      1.00800     0.000       A    0.00000e+00
>     0.00000e+00
>

-- 
==================================================

Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441
http://mackerell.umaryland.edu/~jalemkul

==================================================