Hi Kester - The four dummy atoms carry a mass of 1 a.m.u each, hence the oxygen mass of 11.998.
However, what I don't understand is that the same atom has a mass of 0.0 under [ atomtypes ]. -- The later section overwrites previous one, so it is possible to write zeros for charges and masses in [atomtypes] if you then write correct numbers in [atoms]. I believe this situation is due to historical reasons. For a system consisting of graphene, water and (Na+ OH-, or H3O+ Cl-) ions, if there is nonbonding-parameters specified, will having a different fudge value (0.5 instead of 1.0) make a difference? -- Yes, it will -- but only for graphene. Small particles do not exhibit 1-4 interactions, because they do NOT possess atoms which are separated by 3 covalent bonds, -C-C-C-C-. 1-4 interactions work as a supplement to the dihedral function. To understand which number (0.5 or 1.0 or what you like) works better, you will have to compare dihedrals from MD simulations with those you expect (from X-ray structure, from electronic structure description, etc). Normally, 1-4 interactions do matter, but they don't make a global difference. Best of luck, Vitaly Dr. Vitaly V. Chaban Виталий Витальевич ЧАБАН On Mon, Oct 20, 2014 at 6:13 AM, Kester Wong <kester2...@ibs.re.kr> wrote: > Hi Dr. Chaban, > > > The four dummy atoms carry a mass of 1 a.m.u each, hence the oxygen mass > of 11.998. > > However, what I don't understand is that the same atom has a mass of 0.0 > under [ atomtypes ]. > > > For a system consisting of graphene, water and (Na+ OH-, or H3O+ Cl-) > ions, if there is nonbonding-parameters specified, will having a different > fudge value (0.5 instead of 1.0) make a difference? > > > Thank you in advance. > > > Regards, > > Kester > --------- 원본 메일 --------- > > *보낸사람* : "Dr. Vitaly Chaban" <vvcha...@gmail.com> > *받는사람* : <gmx-us...@gromacs.org> > *받은날짜* : 2014년 10월 18일(토) 16:20:49 > *제목* : Re: [gmx-users] SWM4-NDP force field > > The assigned masses are due to the presence of dummy atoms. The model > molecule must represent moments of inertia. > > 1-4 (fudgeLJ and fudgeQQ) interactions do not apply for water. So, you care > about a larger molecule only. > > > Dr. Vitaly V. Chaban > > Виталий Витальевич ЧАБАН > > > > > On Sat, Oct 18, 2014 at 8:39 AM, Kester Wong wrote: > > > > Dear all, > > > > > > > > I would like to know if this would cause a difference in MD calculations > (text highlighted in red): > > > > The assigned mass for the hydroxide O-atom seems to be inconsistent. Was > the zero atomic mass set with a specific purpose? > > > > > > #define SHELLPTYPE S > > > > #define SHELLMASS 0 > > > > #define OXYGENMASS 15.9994 > > > > > > [ atomtypes ] > > > > ; name btype mass charge ptype sigma epsilon > > > > SWM4-NDP_110a OD SHELLMASS -1.71636 SHELLPTYPE 0.0 > 0.0 > > > > SWM4-NDP_OV1 OV1 1.0 0.0 A 0.24 > 0.294191 > > > > SWM4-NDP_OV2 OV2 0.0 0.0 D 0.28 > 0.294191 > > > > SWM4-NDP_H H 1.008 0.0 A 0.07 > 0.294191 > > > > SWM4-NDP_qH qH 0.0 0.23 D 0.0 0.0 > > > > *SWM4-NDP_O O 0.0 0.203 A 0.0 0.0* > > > > > > > > ; Hydroxide > > > > [ moleculetype ] > > > > ; molname nrexcl > > > > OH- 2 > > > > > > [ atoms ] > > > > ; id at type res nr residu name at name cg nr charge mass > > > > 1 *SWM4-NDP_O 1 OH- O 1 0.202 > > 11.998* > > > > 2 SWM4-NDP_110a 1 OH- OS 1 -1.432 0.00 > > > > 3 SWM4-NDP_H 1 OH- H 1 0.00 1.008 > > > > 4 SWM4-NDP_OV1 1 OH- OV1 1 0.00 1.0 > > > > 5 SWM4-NDP_OV1 1 OH- OV1 1 0.00 1.0 > > > > 6 SWM4-NDP_OV1 1 OH- OV1 1 0.00 1.0 > > > > 7 SWM4-NDP_OV1 1 OH- OV1 1 0.00 1.0 > > > > 8 SWM4-NDP_OV2 1 OH- OV2 1 0.00 0.00 > > > > 9 SWM4-NDP_qH 1 OH- qH 1 0.23 0.00 > > > > > > [ polarization ] > > > > #ifdef POL2WATER > > > > 1 2 2 0.0006809 0.02 16.736e8 > > > > #else > > > > 1 2 1 0.0006809 > > > > #endif > > > > > > ; Initialy developed as a harmonic bond > > > > ; Conversion: alpha=sqrt(qS)/(4*pi*eps0*CAL2J*A2NM*k) = 138.9354492 * > sqrt(qS)/k > > > > ; [ bonds ] > > > > ; 1 2 6 0.0 418400 > > > > > > [ constraints ] > > > > 3 1 1 0.0968 > > > > 4 1 1 0.1463 > > > > 5 1 1 0.1463 > > > > 6 1 1 0.1463 > > > > 7 1 1 0.1463 > > > > 4 6 1 0.1979 > > > > 6 5 1 0.1979 > > > > 5 7 1 0.1979 > > > > 7 4 1 0.1979 > > > > > > #ifdef CONSTRAINTS > > > > [ constraints ] > > > > 3 4 1 0.15 > > > > 3 5 1 0.15 > > > > 3 6 1 0.15 > > > > ; A fourth constraint would make the system redundant and therefore > > > > ; numerically unstable. > > > > ; 3 7 1 0.15 > > > > #else > > > > [ angles ] > > > > 3 1 4 1 73.11 683 > > > > 3 1 5 1 73.11 683 > > > > 3 1 6 1 73.11 683 > > > > 3 1 7 1 73.11 683 > > > > #endif > > > > > > [ dummies2 ] > > > > 8 3 1 1 1.4390 > > > > 9 3 1 1 -0.3099 > > > > > > [ exclusions ] > > > > 1 2 3 4 5 6 7 8 9 > > > > 2 1 3 4 5 6 7 8 9 > > > > 3 1 2 4 5 6 7 8 9 > > > > 4 1 2 3 5 6 7 8 9 > > > > 5 1 2 3 4 6 7 8 9 > > > > 6 1 2 3 4 5 7 8 9 > > > > 7 1 2 3 4 5 6 8 9 > > > > 8 1 2 3 4 5 6 7 9 > > > > 9 1 2 3 4 5 6 7 8 > > > > > > > > If I am to add/define graphene's bonded and nonbonded parameters into the > SWM4-NDP force field, using CHARMM27 parameters, should I take into > consideration the fudgeLJ and fudgeQQ differences (0.5 fudge LJ and fudgeQQ > in SWM4-NDP, 1.0 for fudgeLJ and fudgeQQ in CHARMM27)? The comb-rules are > the same (no.2). > > > > > > > > Thanks in advance! > > > > Kester > -- > Gromacs Users mailing list > > * Please search the archive at > http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! > > * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists > > * For (un)subscribe requests > visithttps://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or > send a mail to gmx-users-requ...@gromacs.org. > > > > -- > Gromacs Users mailing list > > * Please search the archive at > http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before > posting! > > * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists > > * For (un)subscribe requests visit > https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or > send a mail to gmx-users-requ...@gromacs.org. > > -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? 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