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7.1 Single-q calculation

The phonon code ph.x calculates normal modes at a given q-vector, starting from data files produced by pw.xwith a simple SCF calculation. NOTE: the alternative procedure in which a band-structure calculation with calculation='phonon was performed as an intermediate step is no longer implemented since version 4.1. It is also no longer needed to specify lnscf=.true. for q$ \ne$ 0.

The output data file appear in the directory specified by variables outdir, with names specified by variable prefix. After the output file(s) has been produced (do not remove any of the files, unless you know which are used and which are not), you can run ph.x.

The first input line of ph.x is a job identifier. At the second line the namelist &INPUTPH starts. The meaning of the variables in the namelist (most of them having a default value) is described in file Doc/INPUT_PH.*. Variables outdir and prefix must be the same as in the input data of pw.x. Presently you must also specify amass(i) (a real variable): the atomic mass of atomic type i.

After the namelist you must specify the q-vector of the phonon mode, in Cartesian coordinates and in units of 2$ \pi$/a.

Notice that the dynamical matrix calculated by ph.x at q = 0 does not contain the non-analytic term occurring in polar materials, i.e. there is no LO-TO splitting in insulators. Moreover no Acoustic Sum Rule (ASR) is applied. In order to have the complete dynamical matrix at q = 0 including the non-analytic terms, you need to calculate effective charges by specifying option epsil=.true. to ph.x. This is however not possible (because not physical!) for metals (i.e. any system subject to a broadening).

At q = 0, use program dynmat.x to calculate the correct LO-TO splitting, IR cross sections, and to impose various forms of ASR. If ph.x was instructed to calculate Raman coefficients, dynmat.x will also calculate Raman cross sections for a typical experimental setup. Input documentation in the header of PH/dynmat.f90.

A sample phonon calculation is performed in Example 02.


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Next: 7.2 Calculation of interatomic Up: 7 Phonon calculations Previous: 7 Phonon calculations   Contents
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