Re: [gmx-users] Maximum Force constant for Position Restraints
On 2015-04-21 21:40, Alex wrote: No, it does not depend on the system content, aside from the mass of the particle. For a simulation requiring numerical integration in time, there is a limit, and I just estimated it above. For the real world, the limit is that there's no such thing as a harmonic position restraint. :) If you want to be really hardcore about it, and still assume there _is_ such a thing as harmonic restraints, then the timestep of the real world is your Planck's time. :) But it boils down to that if you make the force constant very large you need to make the time step short too which may not be what you want. Alex On Tue, Apr 21, 2015 at 1:36 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Thanks Alex. But then, theoretically, is there no limit? All depends on your system's content, right? 2015-04-21 16:16 GMT-03:00 Alex nedoma...@gmail.com: Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM, Alex nedoma...@gmail.com wrote: I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the Nyquist theorem. I believe GMX tests for high vibrational frequencies according to 20*pi*tau on the left (ten times the period). Hope this helps. Alex On Tue, Apr 21, 2015 at 1:02 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Hi guys! Is there a maximum value of Force Constant for Position restraints? Reading the Manual I could only find the default and the equation to describe it. Best, -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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. -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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. -- David van der Spoel, Ph.D., Professor of Biology Dept. of Cell Molec. Biol., Uppsala University. Box 596, 75124 Uppsala, Sweden. Phone: +46184714205. sp...@xray.bmc.uu.sehttp://folding.bmc.uu.se -- 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.
Re: [gmx-users] Maximum Force constant for Position Restraints
David, that's exactly right. For every timestep value, one can derive the appropriate upper limit for the restraint constant in a somewhat physically sound manner. I am just not entirely sure what was the purpose of the initial question, because for infinite restraint constant, I'd just freeze the particle. Actually, come to think of it, my Planck time estimate for Mother Nature's timestep in vibrating bonds is probably incorrect. Effective bond length over the speed of light is more like it. :) Alex DvdS But it boils down to that if you make the force constant very large you DvdS need to make the time step short too which may not be what you want. -- 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.
Re: [gmx-users] Maximum Force constant for Position Restraints
No, it does not depend on the system content, aside from the mass of the particle. For a simulation requiring numerical integration in time, there is a limit, and I just estimated it above. For the real world, the limit is that there's no such thing as a harmonic position restraint. :) If you want to be really hardcore about it, and still assume there _is_ such a thing as harmonic restraints, then the timestep of the real world is your Planck's time. :) Alex On Tue, Apr 21, 2015 at 1:36 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Thanks Alex. But then, theoretically, is there no limit? All depends on your system's content, right? 2015-04-21 16:16 GMT-03:00 Alex nedoma...@gmail.com: Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM, Alex nedoma...@gmail.com wrote: I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the Nyquist theorem. I believe GMX tests for high vibrational frequencies according to 20*pi*tau on the left (ten times the period). Hope this helps. Alex On Tue, Apr 21, 2015 at 1:02 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Hi guys! Is there a maximum value of Force Constant for Position restraints? Reading the Manual I could only find the default and the equation to describe it. Best, -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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. -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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.
Re: [gmx-users] Maximum Force constant for Position Restraints
I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the Nyquist theorem. I believe GMX tests for high vibrational frequencies according to 20*pi*tau on the left (ten times the period). Hope this helps. Alex On Tue, Apr 21, 2015 at 1:02 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Hi guys! Is there a maximum value of Force Constant for Position restraints? Reading the Manual I could only find the default and the equation to describe it. Best, -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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.
Re: [gmx-users] Maximum Force constant for Position Restraints
Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM, Alex nedoma...@gmail.com wrote: I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the Nyquist theorem. I believe GMX tests for high vibrational frequencies according to 20*pi*tau on the left (ten times the period). Hope this helps. Alex On Tue, Apr 21, 2015 at 1:02 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Hi guys! Is there a maximum value of Force Constant for Position restraints? Reading the Manual I could only find the default and the equation to describe it. Best, -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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.
Re: [gmx-users] Maximum Force constant for Position Restraints
Thanks Alex. But then, theoretically, is there no limit? All depends on your system's content, right? 2015-04-21 16:16 GMT-03:00 Alex nedoma...@gmail.com: Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM, Alex nedoma...@gmail.com wrote: I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the Nyquist theorem. I believe GMX tests for high vibrational frequencies according to 20*pi*tau on the left (ten times the period). Hope this helps. Alex On Tue, Apr 21, 2015 at 1:02 PM, Marcelo Depólo marcelodep...@gmail.com wrote: Hi guys! Is there a maximum value of Force Constant for Position restraints? Reading the Manual I could only find the default and the equation to describe it. Best, -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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? 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. -- Marcelo Depólo Polêto Group of Structural Bioinformatics - Center of Biotechnology Student of MSc Cell and Molecular Biology - UFRGS (Brazil) B.Sc. Biochemistry - University of Viçosa (Brazil) -- 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.
