[Pw_forum] QE & Xcrysden
Giovanni Cantele
giovanni.cantele at na.infn.it
Wed Mar 10 18:15:29 CET 2010
On Mar 10, 2010, at 6:07 PM, naphtaly moro wrote:
> Dear Re: Ngoc Linh Nguyen, Giovanni Cantele & Sebastijan Peljhan
>
> I am working on the various phases of GaAs. at normal conditions, GaAs
> assumes a Zincblende structures fcc ibrav=2, as pressure increases it
> assumes Rocksalt structure and then assumes a CsCl structure which is
> bcc ibrav=3 that is why my input as i posted it. Can you advice me
> further?
> Regards
This is possible, but as I explained, your positions are wrong. Indeed, the atom in 000
will be periodically replicated according to the bcc lattice sites. That means that you have
a Ga atom in 0.5 0.5 0.5 too.
If you specify the As position as 0.5 0.5 0.5 that will be overlapped to the Ga atom end no
code will know what to do.
Therefore, you should understand after the fcc -> bcc transition what changes to the basis
occur, namely the "new" atomic positions in the bcc lattice unit cell.
Giovanni
>
>
>>
>>
>>
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Wed, 10 Mar 2010 11:44:52 +0300
>> From: naphtaly moro <moronaphtaly84 at gmail.com>
>> Subject: [Pw_forum] QE & Xcrysden
>> To: pw_forum at pwscf.org
>> Message-ID:
>> <fe3b32711003100044t31b012aen17eacad01974f4ee at mail.gmail.com>
>> Content-Type: text/plain; charset=ISO-8859-1
>>
>> Dear Q.E. & Xcrysden
>> I am working on the various phase transitions of GaAs. I am trying to
>> contact these structures. I ahve managed to construct the ZB and RS
>> structures with success. I am using Xcrysden with Quantum Espresso.
>> When i try to view the CsCl-GaAs structure, I only see the Ga atoms
>> and with no As atoms in the matrix. Can someone show me please where I
>> am going wrong
>> my input file is this
>> &control
>> prefix='GaAs',
>> pseudo_dir='/home/physics/Desktop/espresso-4.0.5/pseudo'
>> outdir = './tmp',
>> /
>> &system
>> ibrav= 3, celldm(1) =10.2, nat= 2, ntyp= 2,
>> ecutwfc = 12.0,
>> /
>> &electrons
>> /
>> ATOMIC_SPECIES
>> Ga 69.723 Ga.pbe-nsp-van.UPF
>> As 74.9216 As.pbe-n-van.UPF
>> ATOMIC_POSITIONS
>> Ga 0.00 0.00 0.00
>> As 0.50 0.50 0.50
>> K_POINTS {automatic}
>> 4 4 4 0 0 0
>>
>> Thanks
>>
>>
>> --
>> Cecil Naphtaly Moro
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Wed, 10 Mar 2010 10:07:19 +0100
>> From: Ngoc Linh Nguyen <nnlinh at sissa.it>
>> Subject: Re: [Pw_forum] QE & Xcrysden
>> To: PWSCF Forum <pw_forum at pwscf.org>
>> Message-ID: <4B976147.6060104 at sissa.it>
>> Content-Type: text/plain; charset=us-ascii; format=flowed
>>
>> naphtaly moro wrote:
>>> Dear Q.E. & Xcrysden
>>> I am working on the various phase transitions of GaAs. I am trying to
>>> contact these structures. I ahve managed to construct the ZB and RS
>>> structures with success. I am using Xcrysden with Quantum Espresso.
>>> When i try to view the CsCl-GaAs structure, I only see the Ga atoms
>>> and with no As atoms in the matrix. Can someone show me please where I
>>> am going wrong
>>> my input file is this
>>> &control
>>> prefix='GaAs',
>>> pseudo_dir='/home/physics/Desktop/espresso-4.0.5/pseudo'
>>> outdir = './tmp',
>>> /
>>> &system
>>> ibrav= 3, celldm(1) =10.2, nat= 2, ntyp= 2,
>>> ecutwfc = 12.0,
>>> /
>>> &electrons
>>> /
>>> ATOMIC_SPECIES
>>> Ga 69.723 Ga.pbe-nsp-van.UPF
>>> As 74.9216 As.pbe-n-van.UPF
>>> ATOMIC_POSITIONS
>>> Ga 0.00 0.00 0.00
>>> As 0.50 0.50 0.50
>>> K_POINTS {automatic}
>>> 4 4 4 0 0 0
>>>
>>>
>> You are having a wrong input structure. Namely, you chose ibrav= 3 which
>> means BCC lattice, so in a periodic lattice the As atoms will be
>> overlapped by Ga atoms.
>>
>> How to fix the problem. You should again pick up another ibrav value and
>> calculate the Gs and As positions.
>> As far as I know, GaAs lattice have a similarity to diamond lattice, so
>> I suggest ibrav=2, and
>>
>> Ga 0.00 0.00 0.00
>> As 0.25 0.25 0.25
>>
>> Good luck
>>
>> Linh
>>
>>
>>> Thanks
>>>
>>>
>>>
>>
>>
>> --
>> -----------------------------------------------------
>> Nguyen Ngoc Linh, PhD Student
>> c/o: SISSA & CNR-INFM Democritos,
>> via Beirut 2-4, 34014 Trieste (Italy)
>> email: nnlinh at sissa.it
>> phone: +39 04 03787 319
>> skype: ngoclinh84phys
>> -----------------------------------------------------
>> "The physics is theoretical but the fun is real"
>>
>>
>>
>>
>> ------------------------------
>>
>> Message: 4
>> Date: Wed, 10 Mar 2010 10:12:03 +0100
>> From: Giovanni Cantele <giovanni.cantele at na.infn.it>
>> Subject: Re: [Pw_forum] QE & Xcrysden
>> To: PWSCF Forum <pw_forum at pwscf.org>
>> Message-ID: <A01EC0FD-0226-4351-A0A6-040071AACB82 at na.infn.it>
>> Content-Type: text/plain; charset=us-ascii
>>
>>
>> On Mar 10, 2010, at 9:44 AM, naphtaly moro wrote:
>>
>>> Dear Q.E. & Xcrysden
>>> I am working on the various phase transitions of GaAs. I am trying to
>>> contact these structures. I ahve managed to construct the ZB and RS
>>> structures with success. I am using Xcrysden with Quantum Espresso.
>>> When i try to view the CsCl-GaAs structure, I only see the Ga atoms
>>> and with no As atoms in the matrix. Can someone show me please where I
>>> am going wrong
>>> my input file is this
>>> &control
>>> prefix='GaAs',
>>> pseudo_dir='/home/physics/Desktop/espresso-4.0.5/pseudo'
>>> outdir = './tmp',
>>> /
>>> &system
>>> ibrav= 3, celldm(1) =10.2, nat= 2, ntyp= 2,
>>> ecutwfc = 12.0,
>>> /
>>> &electrons
>>> /
>>> ATOMIC_SPECIES
>>> Ga 69.723 Ga.pbe-nsp-van.UPF
>>> As 74.9216 As.pbe-n-van.UPF
>>> ATOMIC_POSITIONS
>>> Ga 0.00 0.00 0.00
>>> As 0.50 0.50 0.50
>>> K_POINTS {automatic}
>>> 4 4 4 0 0 0
>>>
>>> Thanks
>>>
>>>
>>> --
>>> Cecil Naphtaly Moro
>>
>>
>> The reason is that you specify ibrav = 3 that, according to what explained
>> in Doc/INPUT_PW.txt is a bcc lattice.
>> At the same time you give the ATOMIC_POSITIONS in units of the alat (namely,
>> a in bohr units).
>> Therefore, the As atom is placed at (a/2, a/2, a/2) which is, by chance (!),
>> also a site of the bcc lattice.
>> In other words, what XCrysDen sees is a Ga atom in a/2,a/2,a/2 but ALSO an
>> As atom at the same place and decides
>> to delete the latter.
>> Maybe you want to specify the fcc lattice (ibrav=2) and the As atom at
>> a/4,a/4,a/4.
>>
>> Giovanni
>>
>>
>> PS not very sure that ecutwfc = 12.0 whould give you converged results.
>> Also, because you choosed
>> ultrasoft pseudopotentials, you might want also check the ecutrho parameter
>> (by default = 4 * ecutwfc,
>> but larger values are needed when using US pseudo).
>>
>> --
>>
>> Giovanni Cantele, PhD
>> CNR-SPIN and Dipartimento di Scienze Fisiche
>> Universita' di Napoli "Federico II"
>> Complesso Universitario M. S. Angelo - Ed. 6
>> Via Cintia, I-80126, Napoli, Italy
>> Phone: +39 081 676910 - Fax: +39 081 676346
>> Skype contact: giocan74
>>
>> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
>> Web page: http://people.na.infn.it/~cantele
>> http://www.nanomat.unina.it
>>
>>
>>
>> ------------------------------
>>
>> Message: 5
>> Date: Wed, 10 Mar 2010 10:22:31 +0100
>> From: Sebastijan Peljhan <sebastijan.peljhan at ijs.si>
>> Subject: Re: [Pw_forum] QE & Xcrysden
>> To: PWSCF Forum <pw_forum at pwscf.org>
>> Message-ID: <1268212951.2427.22.camel at surf>
>> Content-Type: text/plain; charset="UTF-8"
>>
>> Dear Cecil,
>>
>> On Wed, 2010-03-10 at 11:44 +0300, naphtaly moro wrote:
>>> Dear Q.E. & Xcrysden
>>> I am working on the various phase transitions of GaAs. I am trying to
>>> contact these structures. I ahve managed to construct the ZB and RS
>>> structures with success. I am using Xcrysden with Quantum Espresso.
>>> When i try to view the CsCl-GaAs structure, I only see the Ga atoms
>>> and with no As atoms in the matrix. Can someone show me please where I
>>> am going wrong
>>> my input file is this
>>> &control
>>> prefix='GaAs',
>>> pseudo_dir='/home/physics/Desktop/espresso-4.0.5/pseudo'
>>> outdir = './tmp',
>>> /
>>> &system
>>
>> ibrav = 3 represents bcc cubic cell, hence the Ga and As atoms in your
>> structure overlap. Xcrysden actually warns you, that some of the atoms
>> overlap and they will be deleted.
>>
>> According to QE example06 you should try with ibrav = 2 (fcc) and As
>> atom at (0.25 0.25 0.25) position.
>>
>>
>> Cheers,
>>
>> Sebastijan
>>
>>
>>> ibrav= 3, celldm(1) =10.2, nat= 2, ntyp= 2,
>>> ecutwfc = 12.0,
>>> /
>>> &electrons
>>> /
>>> ATOMIC_SPECIES
>>> Ga 69.723 Ga.pbe-nsp-van.UPF
>>> As 74.9216 As.pbe-n-van.UPF
>>> ATOMIC_POSITIONS
>>> Ga 0.00 0.00 0.00
>>> As 0.50 0.50 0.50
>>> K_POINTS {automatic}
>>> 4 4 4 0 0 0
>>>
>>> Thanks
>>>
>>>
>>
--
Giovanni Cantele, PhD
CNR-SPIN and Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
Phone: +39 081 676910 - Fax: +39 081 676346
Skype contact: giocan74
ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele
http://www.nanomat.unina.it
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