[Wien] How to speed up a reliable optimization
Luis Ogando
lcodacal at gmail.com
Thu Jan 26 15:33:49 CET 2017
Thank you once more !!
Luis
2017-01-26 11:41 GMT-02:00 Laurence Marks <L-marks at northwestern.edu>:
> N.B., the latest release has some additional controls that allow for a bit
> more control of the trust region, e.g. a maximum size. These are in the
> README, they are not in the user guide. They should only be used by experts
> for really nasty to converge problems.
>
> ---
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought", Albert Szent-Gyorgi
> http://www.numis.northwestern.edu
> Corrosion in 4D http://MURI4D.numis.northwestern.edu
> Partner of the CFW 100% gender equity project, www.cfw.org/100-percent
> Co-Editor, Acta Cryst A
>
>
> On Jan 26, 2017 07:28, "Laurence Marks" <L-marks at northwestern.edu> wrote:
>
>> The last two (three) have useful information. They are
>>
>> Mode Size Step
>>
>> Mode is whether the trust region is active; it is off when Newton is
>> shown.
>>
>> Size is the radius of the trust region compared to a full Newton step,
>> for instance 0.5 would mean only half the full radius.
>>
>> Step is the magnitude of the step taken compared to a full Pratt step.
>>
>> All mixer codes (other DFT as well) use a Taylor series expansion for the
>> density change with some approximation for the Jacobian (see the mixer
>> README & papers). MSEC3 & MSR1 use different Jacobian approximations, as
>> did the old BROYD. Neglecting the higher-order terms is only valid for some
>> total step magnitude, the trust-region radius which is the "Size" variable
>> above. When Size is small the algorithm thinks these higher-order terms
>> matter. (The mixer adjusts the trust-region radius depending upon how much
>> the self-consistency is improving, which is very tricky, fuzzy coding and
>> imperfect.)
>>
>> The numbers you sent indicate that the algorithm thinks everything is
>> "fine". If Size is small (e.g. 0.05) and remains small that suggests a
>> problem. The "Step" term can be small when :DIS is large, but should not be
>> small near the solution. If it is large (2-3 or more) the algorithm thinks
>> that there are soft modes present.
>>
>> ---
>> Professor Laurence Marks
>> "Research is to see what everybody else has seen, and to think what
>> nobody else has thought", Albert Szent-Gyorgi
>> http://www.numis.northwestern.edu
>> Corrosion in 4D http://MURI4D.numis.northwestern.edu
>> Partner of the CFW 100% gender equity project, www.cfw.org/100-percent
>> Co-Editor, Acta Cryst A
>>
>>
>>
>> On Jan 26, 2017 05:02, "Luis Ogando" <lcodacal at gmail.com> wrote:
>>
>> Dear Prof. Marks,
>>
>> Just for completeness, in the InP case I am using mBJ and I have
>> checked that during the last 20 regular SCF cycles the steps are changing
>> from
>>
>> :MIX : MSE1 REGULARIZATION: 6.30E-06 GREED: 0.317 Newton 1.00 0.22
>>
>> to
>>
>> :MIX : MSE1 REGULARIZATION: 4.93E-06 GREED: 0.437 Newton 1.00 1.14
>>
>> Thank you once more !
>> All the best,
>> Luis
>> * PS: Could you, please, clarify the meaning of the last two columns in
>> the :MIX line ?
>>
>> 2017-01-26 8:18 GMT-02:00 Luis Ogando <lcodacal at gmail.com>:
>>
>>> Dear Prof. Marks,
>>>
>>> Thank you very much for your answers ! I am pretty sure that your
>>> "intuition" will save a lot of computation time !
>>> Just one last question: I have another system , a supercell formed by
>>> 15 InP zinc blend cells along [111] (hexagonal representation of the cubic
>>> lattice) and 3 InP wurtzite cells. They are aligned along the hexagonal "c"
>>> axis.
>>> Comparing the gaps of the
>>> respective bulks and this supercell (same calculation parameters) , I
>>> believe that the SCF cycle (here, it is not a lattice optimization) stopped
>>> at a local minimum.
>>> My question is : in this case
>>> (regular SCF cycle and InP cells), would you change any of your previous
>>> answers ?
>>> Thank you again !!
>>> All the best,
>>> Luis
>>>
>>>
>>> 2017-01-25 17:56 GMT-02:00 Laurence Marks <L-marks at northwestern.edu>:
>>>
>>>> Inlined is my intuition, which does not have to be completely right.
>>>>
>>>> On Wed, Jan 25, 2017 at 11:32 AM, Luis Ogando <lcodacal at gmail.com>
>>>> wrote:
>>>>
>>>>> Dear Prof. Marks (and Wien2k community),
>>>>>
>>>>> After a recent discussion about "difficult" optimizations in this
>>>>> mailing list (subject: "Mixer surprise when using PBE0 hybrid on-site
>>>>> functional"), I would like ask you for an advice.
>>>>> I have a system with:
>>>>> * 5 rings with C, H and N atoms
>>>>> * 100 atoms with P1 symmetry
>>>>> * the rings are out of a plane
>>>>> * vacuum along y and z
>>>>> I know that this is a very hard optimization problem, so I would
>>>>> like to kindly ask:
>>>>>
>>>>> 1) Do you believe that MSEC3a will work better than MSR1a in such a
>>>>> case ?
>>>>>
>>>>
>>>> I would switch to MSEC3a, use SLOW or reduce the GREED to 0.1 only if
>>>> you see indications of problems. If the system is a decent insulator and
>>>> the experimental positions are quite good you may have no problems. At the
>>>> end I would switch back to MSR1a certainly for a system with OH as the
>>>> positions of the hydrogens can be quite soft. It can take quite some time
>>>> to get the rotations of the OH bond distance right as Wien2k uses cartesian
>>>> coordinates not polars. Which of the 3 is best -- I am not sure.
>>>>
>>>>>
>>>>> 2) Do you recommend using -it, -vec2pratt and -noHinv options with
>>>>> run_lapw ?
>>>>>
>>>>
>>>> I use -it -noHinv -vec2pratt. Sometimes you need to do an occasional
>>>> full diagonalization (touch .fulldiag) as the iterative method is less
>>>> stable (it adds a little noise). In my personal version I have added back
>>>> the old -itn option so this is done automatically every few steps.
>>>>
>>>>>
>>>>> 3) Should I reduce TRUST to 0.5 (I am using LDA and experimental
>>>>> values for the initial atomic positions) ?
>>>>>
>>>>
>>>> Probably not. TRUST 0.5 would be if it is taking much too large steps
>>>> which tends (in my experience) to occur more with soft electronic modes
>>>> such as one has with d and f electrons.
>>>>
>>>>>
>>>>> 4) Should I use SLOW in case.inm ?
>>>>>
>>>>
>>>> See my answer to 1)
>>>>
>>>>>
>>>>> Many thanks in advance.
>>>>> All the best,
>>>>> Luis
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Professor Laurence Marks
>>>> "Research is to see what everybody else has seen, and to think what
>>>> nobody else has thought", Albert Szent-Gyorgi
>>>> www.numis.northwestern.edu ; Corrosion in 4D:
>>>> MURI4D.numis.northwestern.edu
>>>> Partner of the CFW 100% program for gender equity,
>>>> www.cfw.org/100-percent
>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.cfw.org_100-2Dpercent&d=CwMFaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=CZHTnM-OmVb7WVhK4QBSMqumiacPyU-LxrLt8-sw9bU&s=cyXhG2IW3LH9f7wuLmlZGAS47BrtGluAX3LnBa9-Mug&e=>
>>>> Co-Editor, Acta Cryst A
>>>>
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>>>>
>>>>
>>>
>>
>>
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