[Pw_forum] something strange in rutile and anatase calculation
vega
vegalew at hotmail.com
Sat Aug 30 02:39:54 CEST 2008
Dear sir,
Thank you for getting back to me.
>
> I have read the paper and have 2 comments.
I used to think the paper was written by you. Why did you need to read it
again?
> 2. They used only LDA, but not GGA. As it is well known (hopefully I am
> not wrong here) LDA fails for the ground state of Fe. In contrast to this,
> GGA does a good job for Fe.
But I found the sentence like this, 'The generalized gradient approximation
in the Perdew-
Burke-Ernzerhof parametrization was chosen to treat the exchange-correlation
effects.' in the Methods section. I was rather confused.
> So, it will be very good if Vega can calculate the total energies for the
> rutile and anatase phases in odrer to study whether their energy position
> is dependent on the choice of exchange-correlation functional.
I used to do a little test against this. The results suggested that the GGA
overestimate the lattice parameters a little with 1% and LDA underestimate
the lattice parameters for both case. I didn't pay a lot attentions on
energy position calculated by LDA. I'll check it as soon as possible. But to
my best knowledge, there were many reports suggested that the calculated
anatase stability was better than rutile. For example, J. Chem. Phys. 126,
154703 (2007) said 'No matter which Hamiltonian or method is used, the
results on relative stability of both phases suggest that the anatase is
more stable than the rutile phase of TiO2.'. Same conclusion also was
mentioned in Phys. Rev. B 2002, 65 (22) and Phys. Rev. B 2007, 76 et al.
> It might also be that there is a transferability problem for these PsPs (I
> can not prove this, just suggestion).
Because I'm a beginner for QE. I though pseudopotentials is quite
transferable and we could use the same pseudopotentials for any mater
containing the same kind of element. For instance, we could use the same
pseudopotentials for hcp Ti, TiN, rutile, brookite, anatase and other
polymorphs under high pressure, such as Fluorite,Baddeleyite et al. But now,
I think I'm probably wrong. Could you tell me the difference between the Ti
pseudopotentials for hcp-Ti and TiN or many polymorphs of TiO2? And I also
wonder how to judge whether the pseudopotentials is suitable for certain
calculation? to calculate the lattice parameters and compare the results
with the experimental data? Is that enough?
> It is my pleasure that they also mentioned that including of phonon
> contribution might be important.
I would like to calculate the phonon contribution. But I have few knowledge
about it. I'll learn to do that if necessary.
vega
=================================================================================
Vega Lew (weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
--------------------------------------------------
From: "Eyvaz Isaev" <eyvaz_isaev at yahoo.com>
Sent: Saturday, August 30, 2008 7:14 AM
To: "PWSCF Forum" <pw_forum at pwscf.org>
Subject: Re: [Pw_forum] something strange in rutile and anatase calculation
> Dear Wei,
>
> Thanks a lot for bringing the paper to our attention.
>
> I have read the paper and have 2 comments.
>
> 1. They used only norm-conserving pseudopotentials constructed by means of
> different methods.
>
> 2. They used only LDA, but not GGA. As it is well known (hopefully I am
> not wrong here) LDA fails for the ground state of Fe. In contrast to this,
> GGA does a good job for Fe.
>
> So, it will be very good if Vega can calculate the total energies for the
> rutile and anatase phases in odrer to study whether their energy position
> is dependent on the choice of exchange-correlation functional.
>
> It might also be that there is a transferability problem for these PsPs (I
> can not prove this, just suggestion).
>
> It is my pleasure that they also mentioned that including of phonon
> contribution might be important.
>
> Bests,
> Eyvaz.
>
> -------------------------------------------------------------------
> Prof. Eyvaz Isaev,
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
> Russia,
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University,
> Sweden
> Condensed Matter Theory Group, Uppsala University, Sweden
> Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>
>
> --- On Fri, 8/29/08, willy kohn <willykohn at gmail.com> wrote:
>
>> From: willy kohn <willykohn at gmail.com>
>> Subject: Re: [Pw_forum] something strange in rutile and anatase
>> calculation
>> To: "PWSCF Forum" <pw_forum at pwscf.org>
>> Date: Friday, August 29, 2008, 10:02 PM
>> Hi, Vega:
>>
>> A recent result (Jpn. J. Appl. Phys. 39 (2000) L847) showed
>> that different
>> pseudopotential leaded to different conclusions.
>>
>> Best,
>>
>> Wei
>>
>> On Thu, Aug 28, 2008 at 4:28 AM, vega
>> <vegalew at hotmail.com> wrote:
>>
>> > Dear all,
>> >
>> > It is known that the rutile is more stable than
>> anatase in thermodynamics.
>> > Surprisingly, when I did the vc-relax calculation by
>> QE, I found
>> > the calculated energy of anatase lower than rutile.
>> Both vc-relax
>> > calculation for rutile and anatase onverged in 6 scf
>> cycles and 3 bfgs
>> > steps, giving the final enthalpy = -362.7585836890 Ry
>> for rutile and
>> > -725.5447425835 Ry for antase. So the average energy
>> of [TiO2] unit
>> > is -181.3792918445 Ry for rutile and -181.386185645875
>> Ry for anatase. It
>> > looks like anatase is more stable than rutile. Do you
>> think it was quite
>> > strange?
>> >
>> > To make the calculation both for anatase and rutile
>> comparable, I used the
>> > same ecutwfc=40 Ry and ecutwfc=400 Ry, and a quite
>> dense k-point mesh for
>> > both case, 4x4x7 for rutile and 5x5x2 for anatase.
>> >
>> > for better understanding in my calculation, please
>> read the input file
>> > below,
>> > for anatase case,
>> > &CONTROL
>> > title = 'Anatase
>> lattice' ,
>> > calculation = 'vc-relax' ,
>> > restart_mode = 'from_scratch'
>> ,
>> > outdir =
>> >
>> '/home/hjfeng/vega/TiO2/Anatase/lattice/vctest/tmp/'
>> ,
>> > wfcdir = '/tmp/' ,
>> > pseudo_dir =
>> '/home/hjfeng/vega/espresso-4.0/pseudo/' ,
>> > prefix = 'Anatase
>> lattice' ,
>> > disk_io = 'none' ,
>> > nstep = 1000 ,
>> > /
>> > &SYSTEM
>> > ibrav = 6,
>> > celldm(1) = 7.1356,
>> > celldm(3) = 2.5122,
>> > nat = 12,
>> > ntyp = 2,
>> > ecutwfc = 40 ,
>> > ecutrho = 400 ,
>> > /
>> > &ELECTRONS
>> >
>> > /
>> > &IONS
>> > ion_dynamics = 'bfgs' ,
>> > /
>> > &CELL
>> > cell_dynamics = 'bfgs' ,
>> > /
>> > ATOMIC_SPECIES
>> > Ti 47.86700 Ti.pw91-sp-van_ak.UPF
>> > O 15.99940 O.pw91-van_ak.UPF
>> > ATOMIC_POSITIONS crystal
>> > Ti 0.000000000 0.000000000 0.000000000
>> > Ti 0.500000000 0.500000000 0.500000000
>> > Ti 0.000000000 0.500000000 0.250000000
>> > Ti 0.500000000 0.000000000 0.750000000
>> > O 0.000000000 0.500000000 0.042000000
>> > O 0.000000000 0.000000000 0.208000000
>> > O 0.500000000 0.500000000 0.292000000
>> > O 0.000000000 0.500000000 0.458000000
>> > O 0.500000000 0.000000000 0.542000000
>> > O 0.500000000 0.500000000 0.708000000
>> > O 0.000000000 0.000000000 0.792000000
>> > O 0.500000000 1.000000000 0.958000000
>> > K_POINTS automatic
>> > 5 5 2 1 1 1
>> >
>> > for rutile case,
>> >
>> > &CONTROL
>> > title = Rutile_lattice ,
>> > calculation = 'vc-relax' ,
>> > restart_mode = 'from_scratch'
>> ,
>> > outdir =
>> > '/home/vega32/TiO2/rutile/lattice/vcrelax/tmp'
>> ,
>> > wfcdir = '/tmp/' ,
>> > pseudo_dir =
>> '/home/vega32/espresso-4.0.1/pseudo/' ,
>> > prefix = 'Anatase
>> lattice' ,
>> > disk_io = 'none' ,
>> > nstep = 1000 ,
>> > /
>> > &SYSTEM
>> > ibrav = 6,
>> > celldm(1) = 8.6814,
>> > celldm(3) = 0.6441,
>> > nat = 6,
>> > ntyp = 2,
>> > ecutwfc = 40 ,
>> > ecutrho = 400 ,
>> > /
>> > &ELECTRONS
>> >
>> > /
>> > &IONS
>> > ion_dynamics = 'bfgs' ,
>> > /
>> > &CELL
>> > cell_dynamics = 'bfgs' ,
>> > /
>> > ATOMIC_SPECIES
>> > O 15.99940 O.pw91-van_ak.UPF
>> > Ti 47.90000 Ti.pw91-sp-van_ak.UPF
>> > ATOMIC_POSITIONS crystal
>> > O 0.304800000 0.304800000 0.000000000
>> > O 0.695200000 0.695200000 0.000000000
>> > O 0.195200000 0.804800000 0.500000000
>> > O 0.804800000 0.195200000 0.500000000
>> > Ti 0.500000000 0.500000000 0.500000000
>> > Ti 0.000000000 0.000000000 0.000000000
>> > K_POINTS automatic
>> > 4 4 7 1 1 1
>> >
>> > vega
>> >
>> >
>> ==============================================================
>> > Vega Lew ( weijia liu)
>> > PH.D Candidate in Chemical Engineering
>> > State Key Laboratory of Materials-oriented Chemical
>> Engineering
>> > College of Chemistry and Chemical Engineering
>> > Nanjing University of Technology, 210009, Nanjing,
>> Jiangsu, China
>> >
>> > _______________________________________________
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>> >
>> >
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