[Pw_forum] relax vs multiple SCF calculations inconsistency

[sarashs]

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?
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> 
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