[QE-users] Phonons of metal/insulator interfaces: convergence problems

[Christoph Wolf]

Dear all,

I am curious if this is a common problem: when calculating the phonons of
an insulator and a metal I face no problems in slab geometry. But when both
are put together there will always be a q-point where convergence cannot be
reached, for example:

* Computing dynamical matrix for *
*q = (   0.000   0.167   0.000 )*
*   2 Sym.Ops. (no q -> -q+G )*

* G cutoff =  609.4453  (  20928 G-vectors) FFT grid: ( 50, 50,400)*

* number of k points=   144  gaussian smearing, width (Ry)=  0.0100*


*  iter #  15 total cpu time : 24287.3 secs   av.it .:
13.0*
*  thresh= 4.091E-07 alpha_mix =  0.700 |ddv_scf|^2 =  8.763E-11*
*...*

*  iter #  59 total cpu time : 27386.7 secs   av.it .:
11.2*
*  thresh= 5.160E-05 alpha_mix =  0.700 |ddv_scf|^2 =  1.219E-06*

*..*
*  iter # 100 total cpu time : 30214.5 secs   av.it .:
10.8*
*  thresh= 1.000E-02 alpha_mix =  0.700 |ddv_scf|^2 =  4.154E-02*

* End of self-consistent calculation*

* No convergence has been achieved*

Due to the oscillating behavior of ddv_scf I doubt that increasing the
iterations will in the end work.

I tried increasing k points and cutoff well beyond SCF convergence (SCF
shows convergence at 12x12x1 and ecutwfc~80 Ry but I went up to 36x36x1 and
120 Ry.)

&inputph
  prefix   = 'mgo',
  trans= .true.
  epsil= .false.,
  fildyn   = 'mgo.dyn',
  ldisp= .true.
  fildvscf = 'dvscf'
  amass(1) = 107.86820
  amass(2) = 24.30500
  amass(3) = 15.0
  outdir='./',
  nq1=6,  nq2=6,  nq3=1,
  tr2_ph   =  1.0d-12,
 /

The system is MgO stacked on top of Ag. The pseudos are NC from the ONCV
library and work very well for the "pure" Ag and MgO separately.

Any hint is very welcome!

Best,
Chris
-- 
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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Re: [QE-users] Inconsistent energy difference between NEB and seperated geometry optimziation

[Giuseppe Mattioli]

Dear Jibiao Li
0.091 (Ry) * 13.606 = 1.238146 (eV)
The NEB output provides energies in eV! Unless the similarity between  
1.238146 and 1.2405 eV is accidental, this should be the source of the  
reported discrepancy.

HTH
Giuseppe

Quoting jibiaoli :


Hi all,
Recently I performed geometry optimizations for two adsroption  
structures which I used as initial and final images for the  
subsequent NEB calculations. However, I found that the energy  
difference obtaned from the seperated geometry optimizations is  
different from the energy difference  between the initial and final  
images given by the NEB calculation. The former is 0.091 eV  
(consistent with vasp and gpaw calculations) but the latter (1.2405  
eV) is one order higer than the former. What's wrong with my NEB  
calculations?



Best


Jibiao Li
Yantze Normal University, China




GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
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