then the relaxation found a local minimum which is all it is guaranteed to find and by exploring the angular dependence you found a better minimum or at least a configuration oh lower energy. If the other coordinates were not optimized, starting the relaxation from this configuration should lead to a better (local) minimum. I have no idea whether the 5 mRy=70meV barrier is real or an artifact of a noisy landscape due to low cutoff/k-points .
stefano On 19/04/2017 20:16, sarashs wrote: > Yes! there is a tiny barrier of 0.005 Ry > > Arash > > On 2017-04-19 00:20, Stefano de Gironcoli wrote: >> Is there an energy barrier between the minimum found by relax and the >> one you find varying the angle ? >> >> stefano >> (sent from my phone) >> >>> On 18 Apr 2017, at 21:54, sarashs <[email protected]> wrote: >>> >>> They use exactly the same cuttoffs, K-points and everything >>> (unfortunately.) but the near equilibrium energies are slightly less >>> than equilibrium one. For instance for SiOZr angle at equilibrium I >>> get: >>> >>> ! total energy = -245.22924923 Ry >>> Harris-Foulkes estimate = -245.22924923 Ry >>> estimated scf accuracy < 3.9E-12 Ry >>> >>> The total energy is the sum of the following terms: >>> >>> one-electron contribution = -715.79581276 Ry >>> hartree contribution = 369.08543112 Ry >>> xc contribution = -57.16353294 Ry >>> ewald contribution = 158.66552815 Ry >>> Dispersion Correction = -0.02086281 Ry >>> >>> And for SiOZr angle at equiliberium-25 I get: >>> >>> ! total energy = -245.23454839 Ry >>> Harris-Foulkes estimate = -245.23454839 Ry >>> estimated scf accuracy < 1.7E-12 Ry >>> >>> The total energy is the sum of the following terms: >>> >>> one-electron contribution = -739.45020087 Ry >>> hartree contribution = 380.81843421 Ry >>> xc contribution = -57.19470926 Ry >>> ewald contribution = 170.61520075 Ry >>> Dispersion Correction = -0.02327322 Ry >>> >>> Which is similar in terms of total energy but slightly lower and >>> that's >>> weird. Is there anything I can do to force QE to use the same basis >>> set >>> throughout SCF calculations? >>> >>> >>>>> On Tuesday, 18 April 2017 17:10:25 CEST sarashs wrote: >>>>> the other SCF's not have higher energy than the >>>>> equilibrium angle regardless of them being optimized with a >>>>> constraint? >>>>> I mean if the structure is originally relax (which it is) then one >>>>> expects other near equilibrium structures to have higher energies. >>>>> Am >>>>> I >>>>> wrong there? >>>> You are right. >>>> >>>> They should be higher, which usually means less negative. As long as >>>> the same >>>> pseudopotentials, cutoffs, k-points and everything else is used. >>>> >>>> Do they? >>> _______________________________________________ >>> Pw_forum mailing list >>> [email protected] >>> http://pwscf.org/mailman/listinfo/pw_forum >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
