[Pw_forum] Pt bulk phonon calculated by PWSCF 1.2.0

[Hong, SamPyo]

Dear PWSCF users, 
 
a couple of days ago I reported a problem with the anomaly in the bulk
Pt phonon dispersion,
but it was beautifully solved  according to the instruction suggested
below by Stefano de Gironcoli.
Really I could reproduce accurately the anomaly in the bulk Pt phonon
dispersion.
 
Just a small question: during a phonon calculation of a slab consisting
several layers, 
I'm seeing the following messages.  Could any of you explain why I'm
getting these messages?
Can this be a effect on the final result of phonons? 
 
(I say that most of the parameters I'm using are defaults.)
------------------------------------------------------------------------
---------------------------------  
   nbndx  =    56  nbnd   =    55  natomwfc =    56  npwx   =     696
     nelec  =   92.00 nkb   =   121  ngl    =    7557
 
Possibly too few bands at point    1    .00000    .00000    .00000
 
Possibly too few bands at point    2    .04167    .07217    .00000
 
Possibly too few bands at point    8    .08333    .00000    .00000
 
------------------------------------------------------------------------
--------------------------------
 
Thanks a lot.
 
Sampyo

	-----Original Message-----
	From: Stefano de Gironcoli [mailto:degironc at sissa.it] 
	Sent: Friday, March 21, 2003 2:49 AM
	To: pw_forum at pwscf.org
	Subject: Re: [Pw_forum] Pt bulk phonon calculated by PWSCF 1.2.0
	
	
	Phonon anomalies in metals are related to Fermi surface nesting.

	You therefore need to describe correctly the Fermi surface. 
	This imply looking for the limit where degauss->0 (mantaining
good convergence 
	with respect BZ sampling) 
	I suggest you keep a reasonable cutoff (35 or less should be OK
for Pt) and  study 
	instead the phonon dispersion behaviour with respect the degauss
value. 
	Proceed as follow: 
	For each value of degauss you should increase the k point mesh
until frequencies are 
	stable. 
	Look for the behavior of the converged frequency as you reduce
degauss. 

	For not anomalous frequencies things should be rather
insensitive to these details but 
	for the anomalous ones you should see the difference. 

	Have a look to the following two references: 

	S. de Gironcoli, Lattice Dynamics of Metals from
Density-Functional Perturbation Theory,  Phys. Rev. B 51, 6773 (1995). 
	C. Bungaro, S. de Gironcoli, and S. Baroni, Theory of the
anomalous Rayleigh dispersion at H/W(110) surfaces,   Phys. Rev. Lett.
77, 2491 (1996). 

	all the best 

	stefano 

	"Hong, SamPyo" wrote: 

		Hello, dear PWSCF users 

		Recently I calculated the bulk phonons of Pt along
Gamma-K direction. 
		I attached the results in pdf format, where B,C and D
are the ones calculated using PWSCF 1.2.0 version. 
		The open circles are done by a mixed-basis code. The
comparison shows that the frequencies obtained by 
		PWSCF are showing some lowering of frequencies but
oveall it's failing to reproduce the experimentally-observed anomaly in
bulk Pt dispersion 

		along Gamma-K line while a mixed basis program is doing
good job. 
		I used  ecut of 35 ryd for H/Pt US potentials and 72
special k-points. I increased the ecut to 40 ryd but just very slight
changes in frequecies. 

		I also tried higher cut-off for charge density up to 10
times of ecut but just very small changes in frequencies. 

		What else can I try to get better frequencies for bulk
Pt? Could any of you give me some informations ? You will be very
appreciated. 

		Sampyo 

		<<ptbulk2.pdf>>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20030325/0fd63bce/attachment.html>