[Pw_forum] Convergence of Gamma phonon

Subhradip Ghosh subhra at iitg.ernet.in
Fri Feb 4 07:56:18 CET 2005

Dear All,

I have a question regarding convergence of Gamma phonon for metallic

I understand that to check the convergence of Gamma phonon frequencies,
one should test convergence with respect to PW cut-off, k-point mesh,
smearing parameter sequentially.

My question is: what is the criteria for acceptable convergence?

Is it only if the difference in gamma phonon frequencies are ~1% witrh
to all of the above parameters?

Is a higher tolerance(say 3%) for gamma phonons permitted?

I am asking this for a specific reason.

I am doing fcc Copper. For the Gamma phonon, increasing the PW cut-off
upto 60 Ryd hasn't given me convergence ~1%. I am using a k-mesh of
12x12x12 without offset.

It seems strange to me that such a high cut-off is required.

Am I going the wrong way? Should I first look for the convergence with
respect to k-mesh?


			Dr. Subhradip Ghosh
			Assistant Professor
			Department of Physics
		Indian Institute of Technology, Guwahati
			North Guwahati, Assam-781039
			E-mail: subhra at iitg.ernet.in
			Phone: +91 361 2582717(O)
                               +91 361 2584717(R)

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