# Wavevectors for phonons

### This page gives hints on how to set parameters related to the phonon wavevectors (q-points) in DFPT calculations with the ABINIT package.

##### Copyright (C) 2016-2017 ABINIT group (FJ)

Mentioned in topic_Phonons, help_features#6.

### Table of content:

- 1. Introduction.
- 2. Related input variables.

### 1. Introduction.

Like the electronic wavefunctions, the collective atomic displacements that are eigenmodes of the corresponding periodic Hamiltonian can be characterized by a wavevector, denoted q-point.

In ABINIT, DFPT calculations for one dataset are done for one specific q-point, that must be specified. In the simplest case, the user gives the corresponding q-point for each dataset, setting nqpt=1 and specifying the corresponding single qpt. However, very often, it is needed to run calculations for dozens or hundreds of q-points. Hence, the following mechanism has been set: the use can specify a set of q points, using input variables similar to the k-points, and then, for each dataset, the number of the q-point in the set is indicated thanks to iqpt. This applies to the generation of q-point grids as well as to q-point paths to produce phonon band structures.

The input variables for specifying q-points in ANADDB are specified in topic_Phonons and topic_PhononBands.
Go to the top

### 2. Related input variables.

Basic input variables:

... iqpt [Index for QPoinT generation]
... ngqpt [Number of Grid pointsfor Q PoinTs generation]
... nqpt [Number of Q - POINTs]
... qptopt [QPoinTs OPTion]

Useful input variables:

... nshiftq [Number of SHIFTs for Q point grids]
... ph_intmeth [PHonons: INTegration METHod]
... ph_ndivsm [PHonons: Number of DIVisions for sampling the SMallest segment]
... ph_ngqpt [PHonons: Number of Grid points for Q-PoinT mesh.]
... ph_nqpath [PHonons: Number of Q-points defining the PATH]
... ph_nqshift [PHonons: Number of Q-SHIFTs]
... ph_qpath [Phonons: Q-PATH]
... ph_qshift [PHonons: Q-SHIFTs for mesh.]
... ph_smear [PHonons: SMEARing factor]
... ph_wstep [PHonons: frequency(W) STEP.]
... qpt [Q PoinT]
... qptnrm [Q PoinTs NoRMalization]
... qptrlatt [Q - PoinTs grid : Real space LATTice]
... shiftq [SHIFT for Q points]
... wtq [WeighTs for the current Q-points]
Go to the top