[QE-users] Scaling factor for

[Siebe Vanlommel]

Dear Willem and others,

As far as I could infer from the guide alone, that seems to be true. However, I don't understand from the documentation how the A tag is then used if the CELL_PARAMETERS section is provided. From the examples I have tried out, the A tag seems to be simply incompatible with CELL_PARAMETERS as the error persists.

Any references or documentation on what the A tag actually does would be more than welcome as I cannot infer it from the official documentation
Also: any obvious solution to scale the system (either scaling the lattice or even enforcing the volume) is very much appreciated. Editing the structural input parameters is somewhat tedious if this has to be done many times for the same system (e.g. in order to collect E(V) data for an equation of state).

Thanks,
Siebe
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Offermans Willem <willem.offermans at vito.be>
Sent: 08 October 2019 17:24
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Scaling factor for

Dear Siebe and Quantum Espresso friends,

According to me, the tag A in &SYSTEM has a different meaning.

See:

https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm231


Met vriendelijke groeten,
Mit freundlichen Grüßen,
With kind regards,


Willem Offermans
Researcher Electrocatalysis SCT
VITO NV | Boeretang 200 | 2400 Mol
Phone:+32(0)14335263 Mobile:+32(0)492182073

Willem.Offermans at Vito.be<mailto:Willem.Offermans at Vito.be>

[cid:982BA063-B96A-4A1B-89AB-5A01CA9FC70D at vito.local]

On 8 Oct 2019, at 17:07, Siebe Vanlommel <Siebe.Vanlommel at UGent.be<mailto:Siebe.Vanlommel at UGent.be>> wrote:

Hi all,

I am trying to figure out whether there is a way to scale all three unit cell vectors at once in QE using pw.x. In my input file, I am using the CELL_PARAMETERS card (in units of Angstrom) to specify a unit cell. This (https://www.mail-archive.com/users@lists.quantum-espresso.org/msg19387.html) old post seems to suggest that the 'A' parameter in the &SYSTEM section acts as a scaling parameter if 'ibrav==0' and the CELL_PARAMETERS card is used to specify the lattice. I take this to mean that each lattice vector is multiplied by *A, where A is a dimensionless number. However, QE complains that:
"Error in routine cell_base_init (2):
     lattice parameter specified twice"

I've tried specifying the atomic positions in 'crystal' (fractional) coordinates and in Angstroms but to no use. Input file is attached below. I'm using QE version 6.4.1.

Is the interpretation of A as a scaling parameter with these settings deprecated, or am I missing something?

Thanks in advance,
Siebe

input file:

 &CONTROL
                       title = 'cha' ,
                 calculation = 'scf' ,
                  wf_collect = .true. ,
               etot_conv_thr = 1.0D-6 ,
 /
 &SYSTEM
                       ibrav = 0,
                           A = 1.2,
                         nat = 108,
                        ntyp = 2,
                     ecutwfc = 100 ,
                       nosym = .true. ,
 /
 &ELECTRONS
           scf_must_converge = .true. ,
 /
CELL_PARAMETERS angstrom
    13.738516409   -0.000070574    0.000007978
    -6.869319180   11.897869408   -0.000009602
     0.000010055   -0.000007302   14.715552482
ATOMIC_SPECIES
    O   15.99940  O.pbe-rrkjus.UPF
   Si   28.08551  Si.pbe-rrkj.UPF
ATOMIC_POSITIONS crystal
O     0.901932010         0.098069851         0.126854702
O     0.098068745         0.901933544         0.873144107
O     0.901940529         0.803877937         0.126862649
O     0.098062465         0.196127742         0.873139246
(...)
K_POINTS gamma
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