The ABINIT Users Mailing List ( CLOSED )

[ren <opticalcase@gmail.com>]

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
> =====================================
>
>