Dear Alex
Only a comment: Why do you need to be so tightly close to experimental
lattice parameters? They are generally not the final output of a bunch
of simulations. As you are not trying to validate a new functional or
some new correction, your results seem to be close enough to
experimental data to ensure the calculation of further parameters
(DOS, band structure, absorption spectroscopy, conductivity, ...). If
you need *exactly* to work with experimental lattice parameters for
some reason instead, then use experimental values and do not perform
vc-relax but relax calculations. Otherwise, I would start asking which
experimental parameters are you trying to reproduce, e.g., at which
temperature, how many defects were present in the experimental sample,
... And I would answer that a "true experimental value" probably does
not exist...
As you need practical answers and not philosophical ones, I would be
satisfied of a result within 1% from "some measurements"
HTH
Giuseppe
Aleksandra Oranskaia <aleksandra.oransk...@kaust.edu.sa> ha scritto:
Right now I am testing some desperate approaches like increasing
k-points, decreasing mixing_beta together with trust_radii to force
systems to change sightly fro step to step in vc-relax, etc.
I also thought that more precise calculation of stresses (in vc-relx
routine) might help, does anyone have experience with parameters
involved in stress calculations like ecfixed, qcutz, q2sigma?
Best,
Alex.
___
Aleksandra Oranskaia (M.Sc.)
ChemS PhD student, KAUST
Phone: +966 50 1335254
On Apr 6, 2019, at 1:00 PM, users-requ...@lists.quantum-espresso.org wrote:
Send users mailing list submissions to
users@lists.quantum-espresso.org
To subscribe or unsubscribe via the World Wide Web, visit
https://lists.quantum-espresso.org/mailman/listinfo/users
or, via email, send a message with subject or body 'help' to
users-requ...@lists.quantum-espresso.org
You can reach the person managing the list at
users-ow...@lists.quantum-espresso.org
When replying, please edit your Subject line so it is more specific
than "Re: Contents of users digest..."
Today's Topics:
1. vc-relax for orthorhombic systems (Aleksandra Oranskaia)
----------------------------------------------------------------------
Message: 1
Date: Fri, 5 Apr 2019 19:39:39 +0300
From: Aleksandra Oranskaia <aleksandra.oransk...@kaust.edu.sa>
To: Quantum Espresso users Forum <users@lists.quantum-espresso.org>
Subject: [QE-users] vc-relax for orthorhombic systems
Message-ID: <8fca3967-9817-4748-b8d3-34ec6f029...@kaust.edu.sa>
Content-Type: text/plain; charset="iso-8859-1"
Dear QE users and developers,
1 When dealing with orthorhombic systems, I start with space_group
super-tight relaxation of the atomic positions (keeping right
balance in force and scf accuracy, increasing ecutrho plus 100 Ry
than my system actually requires, etc), continue with vc-relax
using dofree = ibrav (and press_thr = 0.0), and Always obtain at
least one lattice constant screwed up (with an error like +/- 0.1 A
as compared to the experimental constant).
I tried 1000 setups for a few systems (varying functionals, vdw
corrections, different pseudo libraries, etc) and have a feeling
that sth is not right with vc-relax: for other than orthorhombic
systems the results match the experimental lattice constants with
an acceptable error.
2 I was wondering how vc-relax work for big orthorhombic unit
cells. I took alpha-S8 (space group 70, so 128 atoms turn into 32
within ibrav = 10 with 8 symmetry elements) and am not satisfied
with any lattice constants: on PBEsol level, error in volume is <1%
as compared to the experimental unit cell, but lattice constants
are like 10.602 (exp: 10.465), 12.937 (exp: 12.866), 24.286 (exp:
24.486) A that do not look acceptable at all :-(
I would hugely appreciate any comments,
Thanks,
Alex.
___
Aleksandra Oranskaia (M.Sc.)
ChemS PhD student, KAUST
Phone: +966 50 1335254
--
This message and its contents, including attachments are intended solely
for the original recipient. If you are not the intended recipient or have
received this message in error, please notify me immediately and delete
this message from your computer system. Any unauthorized use or
distribution is prohibited. Please consider the environment before printing
this email.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.quantum-espresso.org/pipermail/users/attachments/20190405/7ab54d9a/attachment-0001.html>
------------------------------
Subject: Digest Footer
_______________________________________________
users mailing list
users@lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users
------------------------------
End of users Digest, Vol 141, Issue 6
*************************************
--
This message and its contents, including attachments are intended solely
for the original recipient. If you are not the intended recipient or have
received this message in error, please notify me immediately and delete
this message from your computer system. Any unauthorized use or
distribution is prohibited. Please consider the environment before printing
this email.
GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.matti...@ism.cnr.it>
_______________________________________________
users mailing list
users@lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users
