The ABINIT Users Mailing List ( CLOSED )

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

Dear Yee Yan,

 My understanding is the following - if abinit found a space group of
the material, it will conserve the symmetry (until otherwise
requested) during cell relaxation. In other words, 'a' would be always
equal 'b' for your case.

jess.

On Wed, Mar 25, 2009 at 7:01 AM, ren <opticalcase@gmail.com> wrote:
> Hi Dr Kondor:
>
> I have not tried optcell 2 yet. Because of the symmetry problem in my
> materials where a=b must be constrained, i tried to search the forum
> to see if anyone would verify optcell=2 could do this but seem none
> talk about it. So i have a little doubt and decide to try other method
> first before hitting on this option. My bad.. my apology.
>
> Cheers,
> Yee Yan
>
> On Tue, Mar 24, 2009 at 7:49 PM, Jess Kondor <kondor.jess@gmail.com> wrote:
>> 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 ]
>>>>
>>>>
>>>
>>>
>>
>>
>>
>> --
>> =====================================
>> Jess Kondor
>>
>> NSTI
>> =====================================
>>
>>
>
>




-- 
=====================================
Jess Kondor

NSTI
=====================================