[Pw_forum] relax vs multiple SCF calculations inconsistency

[stefano de gironcoli]

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 <sarashs at ece.ubc.ca> 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
>>> Pw_forum at pwscf.org
>>> http://pwscf.org/mailman/listinfo/pw_forum
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum