Dear Justin, Thanks for reply and explanation, and..:
>> you've got an amide flanked by two methylene groups as the repeat unit >> All the amino acids in the aminoacids.rtp file specify impropers centered on the C and N atoms of the peptide bond. I meant to say its easy to define (in general) impropers for chiral centers, but not sure about bonds (here peptide). In oplsaa.ff I just looked ALA in aminoacids.rtp for which there are two impropers. ALA impropers: -C CA N H improper_Z_N_X_Y CA +N C O improper_O_C_X_Y which should be as follows: H CH3 H I I I (-)C---------N--CA--C-------N(+) I I I O H O ^ ^ ^ ^ ^ ^ [-C]---------[ALA]-------[N+] Does this mean both improper terms are making peptide bond planar (two peptide bonds: left side and right side of ALA), but in my case as you noticed there are two methylene groups. So is it correct if I define improper for my polymer as: C C2 N H C1 N C O thanks regards, Jiom On Wed, Jul 17, 2013 at 6:51 PM, Justin Lemkul <jalem...@vt.edu> wrote: > > > On 7/17/13 11:39 AM, gromacs query wrote: > >> Dear Justin, >> >> 1) I can understand the improper for stereocenters (chiral) easily but >> with >> > > OPLS doesn't use impropers for chiral centers. > > > bonds I am confused (I have tried to explain below please let me know if I >> have defined impropers correctly for peptide to keep it planar). >> >> H1 O H3 >> \ I / >> --C1---C--N---C2-- >> / I \ >> H2 H H4 >> >> >> > OK, funky text drawing :) But it looks like you've got an amide flanked > by two methylene groups as the repeat unit. > > > So I think improper (being zero) to keep peptide planar should be defined >> (and sufficiently) as: O C N C1 >> and dihedral should be which is simple as: O C N H >> >> But it confuses me, why one needs to define improper for peptide. If I >> just >> keep dihedral angle strict (high force constant) then it will make peptide >> freezed! so it will remain planar. >> >> > The OPLS approach for amides is to define normal dihedrals as well as > impropers. Keep in mind that rotations about a bond and out-of-plane > bending are different types of motion. I suppose you could achieve what > you're thinking of by very strong force constants for the dihedrals, but I > would wonder if you're then throwing the balance of 1-4 interactions > (especially charges) out of whack. > > > 2) Also, I am not sure whether OPLS needs this peptide bond to be defined >> with improper, someone have experienced this please suggest? >> >> > All the amino acids in the aminoacids.rtp file specify impropers centered > on the C and N atoms of the peptide bond. I would stick with that approach. > > > -Justin > > -- > ==============================**==================== > > Justin A. Lemkul, Ph.D. > Postdoctoral Fellow > > Department of Pharmaceutical Sciences > School of Pharmacy > Health Sciences Facility II, Room 601 > University of Maryland, Baltimore > 20 Penn St. > Baltimore, MD 21201 > > jalemkul@outerbanks.umaryland.**edu <jalem...@outerbanks.umaryland.edu> | > (410) > 706-7441 > > ==============================**==================== > -- > gmx-users mailing list gmx-users@gromacs.org > http://lists.gromacs.org/**mailman/listinfo/gmx-users<http://lists.gromacs.org/mailman/listinfo/gmx-users> > * Please search the archive at http://www.gromacs.org/** > Support/Mailing_Lists/Search<http://www.gromacs.org/Support/Mailing_Lists/Search>before > posting! > * Please don't post (un)subscribe requests to the list. Use the www > interface or send it to gmx-users-requ...@gromacs.org. > * Can't post? Read > http://www.gromacs.org/**Support/Mailing_Lists<http://www.gromacs.org/Support/Mailing_Lists> > -- gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting! * Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists