[QE-users] help with turbo-davidson not converging

Fri Jun 26 17:00:14 CEST 2020

Dear Gabriele,

> Things that I have tried (with no joy, and, I must admit, without knowing very well what I was doing):

That's the main problem! You should start exactly from this point. You need to understand every step you do, otherwise what is the point?

I would recommend to go through the tutorial about TDDFPT:

http://indico.ictp.it/event/7921/session/325/contribution/1280/material/0/0.pdf

What is your input for PW calculation? In the links that you provided there is no one pointing to the PW input. But from the PW output it seems that you are using the VdW correction - do you really need it? For an isolated molecule there is no need in the VdW correction. So maybe it would be useful also to go through tutorials on basic PW calculations:

http://indico.ictp.it/event/7921/other-view?view=ictptimetable

http://qe2019.ijs.si/program.html

Greetings,

Iurii

--
Dr. Iurii Timrov
Postdoctoral Researcher
STI - IMX - THEOS and NCCR - MARVEL
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of balducci at units.it <balducci at units.it>
Sent: Friday, June 26, 2020 4:04:26 PM
To: users at lists.quantum-espresso.org
Subject: [QE-users] help with turbo-davidson not converging

hello

I'm having convergence problems with a turbo-davidson calculation on
an isolated (neutral) molecule of a Ru complex:

http://www.dscf.units.it/~balducci/tmp/turbo-davidson-problem/XEDFAQ_1.png

I have limited experience with this kind of calcs, but some time ago I
did similar calcs on another molecule of the same type without any
apparent problem (see also below).

So far my protocol is:
=> geometry relaxation of the isolated molecule (cubic cell (a=21.50
   ang) with a minimum inter-image distance of 10.1 ang, gamma
   point)
=> scf calculation with nbnd=120 (there are 96 occupied bands)
   http://www.dscf.units.it/~balducci/tmp/turbo-davidson-problem/scf.in.txt
=> turbo-davidson run:
   http://www.dscf.units.it/~balducci/tmp/turbo-davidson-problem/davidson.in.txt

    ----8<----
    &lr_input
        outdir='./tmp',
        restart=.false.
    /
    &lr_dav
        p_nbnd_occ=10
        p_nbnd_virt=10
        num_init=60
        num_eign=25
        num_basis_max=200
        residue_conv_thr=1.0E-4
        start=0.18866813     ! 483 nm
        finish=0.23792873    ! 383 nm
        step=0.001
        reference=0.21021155 ! 433.5 nm
        broadening=0.005
        poor_of_ram=.true.
        poor_of_ram2=.true.
        lplot_drho=.true.
    /
    ----8<----

As said, the turbo-davidson calculation doesn't seem to be going
anywhere; here is a typical pattern of the "Largest residue" figure vs
n. of iterations:

http://www.dscf.units.it/~balducci/tmp/turbo-davidson-problem/convergence.png

and here is an output:

http://www.dsch.univ.trieste.it/~balducci/tmp/turbo-davidson-problem/davidson.out.txt

Things that I have tried (with no joy, and, I must admit, without
knowing very well what I was doing):
=> increase num_init
=> decrease num_eign
=> decrease the energy range (start,finish)
=> increase num_basis_max
=> switch vdW-DF off in the scf run
=> increase p_nbnd_occ and p_nbnd_virt

The only way I could get a converged result so far has been to request
a single eigenvalue (num_eign=1): however, I guess this is simply
extreme tweaking of the calculation: even in this conditions, it took
some 22 iterations to converge, which seems too much to me.

I have tried to reproduce my previous calc (the one which worked
smoothly) since qe version at the time was different (I'm presently
using qe-6.5); the molecule was this (ionic species, charge +2):

http://www.dscf.units.it/~balducci/tmp/turbo-davidson-problem/fbt1805_1.png

With the following input:

    ----8<----
    &lr_input
        outdir='./tmp',
        restart=.false.
    /
    &lr_dav
        p_nbnd_occ=10
        p_nbnd_virt=10
        num_init=60
        num_eign=25
        num_basis_max=200
        residue_conv_thr=1.0E-4
        start=0.15
        finish=0.185
        step=0.001
        broadening=0.005
        reference=0.1675
        poor_of_ram=.true.
        poor_of_ram2=.true.
        lplot_drho=.true.
    /
    ---->8----

the calculation converges straightforwardly with qe-6.5:

    ----8<----
    Largest residue:           0.051299398950
    Largest residue:           0.014049254805
    Largest residue:           0.005898374852
    Largest residue:           0.002998212328
    Largest residue:           0.003119825980
    Largest residue:           0.001028311667
    Largest residue:           0.000741910032
    Largest residue:           0.000399386757
    Largest residue:           0.000545167736
    Largest residue:           0.000146498010
    Largest residue:           0.000098106072
    ---->8----

I'm out of ideas and hoping that someone on the list can give me a
clue (apologies: I realize that the statement of the problem is rather
vague, but I don't know how to be more precise than this)

Needless to say, I will be happy to provide any further information
which might be useful

thanks a lot in advance for any hint/suggestion

ciao
-gabriele

--
Gabriele Balducci - Dipartimento di Scienze Chimiche e Farmaceutiche - Via
L. Giorgieri 1 I-34127 TRIESTE tel: I-040-5583957 fax: I-040-5583903 e-mail:
balducci at units.it Please, if possible, don't send me MS Word or PowerPoint
attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html
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