The ABINIT Users Mailing List ( CLOSED )

[Jess Kondor <kondor.jess@gmail.com>]

Hello,

 May be I wrong, but why you don't use an automatic cell optimization
(optcell=2) combined with ionic relaxation (ionmov=2) for your
purpose?

jess


On Mon, Mar 23, 2009 at 2:01 PM, ren <opticalcase@gmail.com> wrote:
> Dear Prof Zwanziger, Dr Matthieu and Dr Dong:
>
> Thank you for your valuable advices! My apology for the late reply.
>
> I did some preliminary work on increasing the Ecut and no of kpts, the
> results seems to be better.
>
> I will work on using optcell=2 as well as strtarget to see how's the result.
>
> Thanks once again!
>
> Cheers
> Yee Yan
>
>
> On Sun, Mar 22, 2009 at 2:52 AM, St Druid <tq02ksu@gmail.com> wrote:
>> Hello users:
>>
>> Invariance of lattice parameter a and b is determined by the symmetry,
>> unless you set the "nsym = 1 ",  according to the origin of the E-V
>> curve, I would like to suggest that, setting optcell = 2, and serial
>> strtarget values to obtain deferent volumes, than plot it.
>>
>> Regards.
>>
>> On Sat, Mar 21, 2009 at 10:14 AM, ren <opticalcase@gmail.com> wrote:
>>> Dear All:
>>>
>>> I am doing geometry optimization for ZnO which has a hexagonal
>>> geometry. The lattice a and b is equal. Therefore, a and b should
>>> change by the same amount. Since it has a space group of P63 mc,
>>> therefore, only the oxygen atoms is able to vary in its z (or u i
>>> suppose) direction , internal coordinate.
>>>
>>> I read up the optimization notes  by L. D. Marks, which is meant for
>>> Wien2k, but i guess it should be applicable universally. What is done
>>> is that, having 5 different volumes having the same a:b:c ratio, the
>>> internal coordinates are optimized. Thereafter, for 5 c/a ratio, each
>>> with 5 different volume, the internal coordinate are optimized.
>>>
>>> At the moment, I tried the first step. But I tried exploring a larger
>>> range of volumes (26 different volumes). By plotting the volumes vs
>>> total energy, it appears that there is 2 local minimal (See the
>>> picture attached. I supposed one would choose the minimal with the
>>> lowest energy ? The volume obtained for the lowest energy is
>>> 313.992080 bohr^3. The other local minimal with a higher energy has a
>>> volume of 294.765030 bohr^3
>>>
>>> The problem occurs when I tried to use optcell=1 to see one could get
>>> similar result. It appears that the result obtained has a optimized
>>> volume similar to 294.765030 bohr^3 which has an energy similar to the
>>> local minimal that has a higher energy as obtained from my first
>>> study. I have also attached the email with both input files together.
>>>
>>> For optcell=1, here is the options i used
>>>
>>> optcell 1 # with optimization of volume only, do not modify rprim and
>>> allow an homogeneous dilation of the 3 component of acell
>>> ionmov 2 # Broyden Steps
>>> ntime 40
>>> dilatmx 1.05
>>> ecutsm 0.5
>>> tolmxf 5.0d-5
>>> toldff 5.0d-6
>>>
>>> I am using Troullier-Martins psp.
>>>
>>> I tried to increase ntime, tolmxf to 5.0d-7 and toldff to 5.0d-7 but
>>> the same results are obtained.
>>>
>>> May I know if anyone can advised me what i have missed out that caused
>>> this discrepancy?
>>> Should using optcell=1 be more accurate than manually optimized the
>>> internal coordinate with different volumes with fixed a:b :c ratio?
>>>
>>> Lastly, i read from the mailing list and it is always recommended to
>>> use optcell=2? Because of this spacegroup, does anyone have experience
>>> that optcell=2 ensure that lattice a=b always expand and contract by
>>> the same amount and that only the z internal coordinate is optimized?
>>>
>>> Hope like to hear from your advices!!
>>>
>>> Sorry for the lengthy email.
>>>
>>> Cheers,
>>> Yee Yan
>>> School of Materials Science and Engineering
>>> Nanyang Technological University (Singapore)
>>>
>>
>>
>>
>> --
>> B.W Dong
>> State Key Laboratory of Superhard Material
>> jilin university, Changchun Jilin, China. 130012
>>
>> tq02ksu@gmail.com [ tq02ksu@email.jlu.edu.cn ]
>>
>>
>
>



-- 
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Jess Kondor

NSTI
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