Hi Francisco I’m afraid I don’t know what this may be due to. Maybe somebody out there does.
If that is not the case: It could be a bug or some still unexplored interaction of features (e.g. md with this particular set of SCF options). It could also be something intrinsic to the problem, not related to the code per se, but rather an instability in your dynamical system. I would suggest first checking as much as possible (controlling CG max cg displacement, seeing whether the energy is consistent with the forces (does it go up by a lot in that step?etc), changing the SCF settings, tightening convergence and changing the scheme,…) If it persists and with the info obtained, cold you please report it as a bug in http://launchpad.net/siesta <http://launchpad.net/siesta> ? Please be as specific and complete as possible. (there is some guidance there) Sorry I cannot be of more help Emilio > On 7 Apr 2017, at 19:11, Francisco Garcia <[email protected]> wrote: > > Hello users: > > I am running a molecular dynamics simulation with SIESTA and the job keep > running into situations where the forces grow large all of a sudden and then > it will go back to normal in the next time step. > > For example: take a look below at the maximum atomic force printed for the MD > steps [this is not the entire trajaectory; I am just showing a tiny segment > to illustrate this problem]. > > Max 8.169457 constrained > Max 7.725134 constrained > Max 7.231393 constrained > Max 6.698717 constrained > Max 6.434356 constrained > Max 180.612893 constrained <--------- large force of 180.61 eV/Ang here > Max 6.351384 constrained > Max 6.500315 constrained > Max 6.616196 constrained > Max 6.705574 constrained > Max 7.375029 constrained > Max 7.971425 constrained > Max 8.440149 constrained > Max 8.768627 constrained > > > Now take a look at the SCF loop for the MD step where the large force was > generated: > > iscf Eharris(eV) E_KS(eV) FreeEng(eV) dDmax > Ef(eV) dHmax(eV) > scf: 1 -217188.442539 -217204.666859 -217206.302454 0.064243 > -1.492048 5.165406 > scf: 2 -146020.001861 -193579.811302 -193580.989056 1.710060 > -0.338743357.676349 > scf: 3 -217800.695121 -217208.716553 -217210.351765 1.701213 > -1.495349 6.087548 > scf: 4 -217213.535597 -217211.812703 -217213.449302 0.032944 > -1.494384 2.570971 > scf: 5 -217212.451595 -217212.518659 -217214.156524 0.027437 > -1.493541 0.659157 > scf: 6 -217212.666366 -217212.617779 -217214.255836 0.005069 > -1.493661 0.297730 > scf: 7 -217212.671543 -217212.651068 -217214.289179 0.002601 > -1.493708 0.171617 > scf: 8 -217212.670437 -217212.664758 -217214.302857 0.002015 > -1.493723 0.141605 > scf: 9 -217212.676500 -217212.671768 -217214.309790 0.001025 > -1.493792 0.096767 > scf: 10 -217212.679444 -217212.676034 -217214.314015 0.000846 > -1.493810 0.083722 > scf: 11 -217212.682014 -217212.679321 -217214.317264 0.000677 > -1.493834 0.059076 > scf: 12 -217212.684219 -217212.682043 -217214.319956 0.000602 > -1.493864 0.037595 > scf: 13 -217212.684718 -217212.683469 -217214.321359 0.000377 > -1.493896 0.032728 > scf: 14 -217212.685645 -217212.684620 -217214.322474 0.000429 > -1.493929 0.029768 > scf: 15 -217212.686201 -217212.685444 -217214.323249 0.000401 > -1.493955 0.027512 > scf: 16 -217212.687024 -217212.686259 -217214.323994 0.000466 > -1.493982 0.024955 > scf: 17 -217212.687903 -217212.687112 -217214.324756 0.000566 > -1.494013 0.021878 > scf: 18 -217212.688413 -217212.687788 -217214.325350 0.000508 > -1.494041 0.018827 > scf: 19 -217212.689186 -217212.688519 -217214.325984 0.000660 > -1.494070 0.014994 > scf: 20 -217212.689633 -217212.689113 -217214.326468 0.000768 > -1.494101 0.010350 > scf: 21 -217212.689427 -217212.689275 -217214.326592 0.000290 > -1.494111 0.008499 > scf: 22 -217212.689461 -217212.689369 -217214.326663 0.000185 > -1.494118 0.006871 > scf: 23 -217212.689521 -217212.689448 -217214.326723 0.000161 > -1.494124 0.006698 > scf: 24 -217212.689528 -217212.689492 -217214.326755 0.000075 > -1.494126 0.006319 > scf: 25 -217212.689561 -217212.689528 -217214.326778 0.000063 > -1.494128 0.005641 > scf: 26 -217212.689564 -217212.689544 -217214.326788 0.000047 > -1.494127 0.004544 > scf: 27 -217212.689564 -217212.689554 -217214.326799 0.000053 > -1.494124 0.003604 > scf: 28 -217212.689567 -217212.689561 -217214.326808 0.000053 > -1.494119 0.002869 > scf: 29 -217212.689568 -217212.689565 -217214.326817 0.000059 > -1.494113 0.002762 > scf: 30 -217212.689569 -217212.689567 -217214.326822 0.000037 > -1.494108 0.002618 > scf: 31 -217212.689566 -217212.689567 -217214.326826 0.000028 > -1.494103 0.002409 > scf: 32 -217212.689566 -217212.689567 -217214.326831 0.000032 > -1.494099 0.002048 > scf: 33 -217212.689569 -217212.689568 -217214.326835 0.000038 > -1.494095 0.001620 > scf: 34 -217212.689576 -217212.689572 -217214.326839 0.000037 > -1.494093 0.001183 > scf: 35 -217212.689582 -217212.689577 -217214.326841 0.000025 > -1.494093 0.000872 > > SCF Convergence by DM+H criterion > max |DM_out - DM_in| : 0.0000250455 > max |H_out - H_in| (eV) : 0.0008717786 > SCF cycle converged after 35 iterations > > Using DM_out to compute the final energy and forces > No. of atoms with KB's overlaping orbs in proc 0. Max # of overlaps: 222 > 160 > > siesta: E_KS(eV) = -217212.6890 > > siesta: Atomic forces (eV/Ang): > ---------------------------------------- > Tot -87.051127 -112.933365 -273.703901 > ---------------------------------------- > Max 180.612893 > Res 19.109629 sqrt( Sum f_i^2 / 3N ) > ---------------------------------------- > Max 180.612893 constrained > > > As far as I can tell, there is nothing wrong in the SCF convergence but yet > still the forces shoot up suddenly and then goes back to normal in the next > step. This causes the temperature to shoot up and throws the system out of > equilibrium for a while, resulting in an increase in the total energy (energy > conservation is destroyed). It also occurs a couple of times. Could this be > an eggbox effect? > > Thank you. > > PS: I am using the latest version of SIESTA > > -- Emilio Artacho Theory of Condensed Matter, Department of Physics Cavendish Laboratory, University of Cambridge J J Thomson Avenue, Cambridge CB3 0HE, UK +44 1223 337461; http://www.tcm.phy.cam.ac.uk/profiles/ea245/
