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optic input variables

This document lists and provides the description of the name (keywords) of the optic input variables to be used in the input file for the optic executable.

broadening

Mnemonics: BROADENING
Mentioned in topic(s): topic_Optic
Variable type: real
Dimensions: scalar
Default value: 1.d-3 Ha
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter applies a broadening to the spectrum and is used to avoid divergences in the sum-over-states approach. The sum-over-states approach to the linear and nonlinear susceptibilities inevitably include resonant denominators of the form \((\omega - \omega_{nm})^{-1}\), see for example Eq. 46 of [Sharma2004]. Numerically these denominators lead to infinities. In order to avoid them one could do one of two things. One could change the sum over k-points to integration, and then use the linear tetrahedron method (see [Hughes1996] for details). Another way to get around the problem, as we will do in the present case, is to avoid the singularities by adding a small imaginary contribution to the denominator. This addition prevents the denominator from ever going to 0, and acts as a broadening to the spectrum. The broadening should not be too large, as this would wash out the features in the spectrum.

ddkfile

Mnemonics: DDK FILE
Mentioned in topic(s): topic_Optic
Variable type: string
Dimensions: scalar
Default value: None
Comment: no default
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the name of the file containing the matrix elements of the \(d/dk\) operator in direction X, as the string ddkfile_X. This file should have been produced by a preparatory Abinit run. This file must not contain the first-order wavefunctions, and may be generated using prtwf 3.

Important

Make sure that the number of bands, spin channels, and k-points are the same in all the files.

domega

Mnemonics: Delta OMEGA
Mentioned in topic(s): topic_Optic
Variable type: real
Dimensions: scalar
Default value: 1.d-3 Ha
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the step size \(\Delta\omega\) for the grid over which the optic utility computes the susceptibilities. The maximum energy is set by the companion parameter maxomega. The susceptibilities are thus computed at maxomega/domega energy points (zero excluded). In order to capture more features, decrease the step size to get a finer energy grid. In order to go to higher frequency, increase the maximum.

lin_comp

Mnemonics: LINear COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: ([‘num_lin_comp’])
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the directions of the num_lin_comp requested components of the dielectric tensor. The components are specified in cartesian coordinates, where 1, 2, and 3 represent x, y, and z respectively. For example, 11 represents the xx component, and 32 represents zy. There should be num_lin_comp entries. Note that these directions are denoted by \(a\) and \(b\) in [Sharma2004].

linel_comp

Mnemonics: LINear ELectro-optic COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: ([‘num_linel_comp’])
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the directions of the num_linel_comp requested components of the linear electro-optical susceptibility. The components are specified in cartesian coordinates, where 1, 2, and 3 represent x, y, and z respectively. For example, 111 represents the xxx component, and 321 represents zyx. There should be num_linel_comp entries.

maxomega

Mnemonics: MAXimum value of OMEGA
Mentioned in topic(s): topic_Optic
Variable type: real
Dimensions: scalar
Default value: 1 Ha
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the maximum energy for the grid over which the optic utility computes the susceptibilities. The grid step size is set by the companion parameter domega. The susceptibilities are thus computed at maxomega/domega energy points (zero excluded). In order to capture more features, decrease the step size to get a finer energy grid. In order to go to higher frequency, increase the maximum.

nband_sum

Mnemonics: Number of BANDs in SUM
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: scalar
Default value: None
Comment: -1 i.e. use all bands found in external files.
Added in version: 9.6.2

Test list (click to open). Rarely used, [0/14] in all optic tests, [0/3] in optic tutorials

This variable specifies the number of bands included in the sum over states expressions. If not given in input, all the bands found in the external files are used.

This option can be used to perform convergence studies with respect to the number of bands for fixed BZ sampling without having to perform multiple calculations from scratch just to change the number of states. The idea is very simple: compute the WFK and the DDK files with a sufficiently large number of bands then use nband_sum to change this parameter when running optic.

Obviously nband_sum cannot be greater than the number of bands stored on disk.

nonlin_comp

Mnemonics: NON-LINear COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: ([‘num_nonlin_comp’])
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the directions of the num_nonlin_comp requested components of the second-order nonlinear dielectric tensor. The components are specified in cartesian coordinates, where 1, 2, and 3 represent x, y, and z respectively. For example, 111 represents the xxx component, and 321 represents zyx. There should be num_nonlin_comp entries. Note that these directions are denoted by \(a\) and \(b\) in [Sharma2004].

num_lin_comp

Mnemonics: NUMber of LINear COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: scalar
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies how many components (out of 9 possible) of the linear optical dielectric tensor to calculate. Some of these may be either equal to each other, or zero, depending upon the symmetry of the material (for details see [Draxl2006]). The directions of the requested components are specified by the parameter lin_comp.

num_linel_comp

Mnemonics: NUMber of LINear ELetro-optic COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: scalar
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies how many components (out of 27 possible) of the linear electro-optical susceptibility to calculate. Some of these may be either equal to each other, or zero, depending upon the symmetry of the material. The directions of the requested components are specified by the parameter linel_comp.

num_nonlin_comp

Mnemonics: NUMber of NON-LINear COMPonents
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: scalar
Default value: 0
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies how many components (out of 27 possible) of the second-order nonlinear optical tensor to calculate. Some of these may be either equal to each other, or zero, depending upon the symmetry of the material. The directions of the requested components are specified by the parameter nonlin_comp.

prtlincompmatrixelements

Mnemonics: PRinT the LINear COMPonent of the dielectric tensor’s MATRIX ELEMENTS
Mentioned in topic(s): topic_Optic
Variable type: integer
Dimensions: scalar
Default value: 0
Added in version: v9.5

Test list (click to open). Moderately used, [1/14] in all optic tests, [0/3] in optic tutorials

If set to 1, the matrix elements, the renormalized (but unshifted) Kohn-Sham eigenvalues, the occupations and the kpts weights are all printed out in the ‘_OPTIC.nc’ file generated by the optic tool. The matrix elements are the ones used to build the linear components of the dielectric tensor. Useful for post processing of matrix elements or rebuild the linear components of the dielectric tensor in an external script.

scissor

Mnemonics: SCISSOR operator
Mentioned in topic(s): topic_Optic
Variable type: real
Dimensions: scalar
Default value: 0.0
Comment: in Ha
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter provides a fixed shift to all the conduction bands. As LDA/GGA are known to underestimate the band-gap by a significant amount in some cases, in order to obtain a reasonable optical spectrum and make a realistic comparison with experiments one needs to correct for this [Levine1989]. The scissors shift is normally chosen to be the difference between the experimental and theoretical band-gap, and simply shifts the conduction bands. Alternatively, one may determine the self energy using the GW approach, in which case the opening of the gap due to the GW correction can be used as the scissor shift.

tolerance

Mnemonics: TOLERANCE
Mentioned in topic(s): topic_Optic
Variable type: real
Dimensions: scalar
Default value: 1.d-3 Ha
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter sets a scale for discarding small energy denominators. When energy denominators are smaller than tolerance, the term is discarded from the sum. See also broadening.

wfkfile

Mnemonics: WaveFunction K FILE
Mentioned in topic(s): topic_Optic
Variable type: string
Dimensions: scalar
Default value: None
Comment: no default
Added in version: before_v9

Test list (click to open). Very frequently used, [14/14] in all optic tests, [3/3] in optic tutorials

This parameter specifies the name of the ground state wavefunction file, which should have been produced in a preparatory Abinit run. It should include both the valence and conduction states to be used in the optic calculation (see optic help file).