This file explains the i/o parameters needed for the calculation of the frequency dependent linear optical dielectric function and second order nonlinear optical susceptibility, in the RPA approximation (sum over states using independent electronic states) thanks to the Optic utility of the ABINIT package.
The user is advised to be familiar with the main abinit help file before reading the present file.
A knowledge of the computation of the linear response d/dk perturbation, explained in the ABINIT (respfn) help file, is also requested. Actually, a full understanding of the ABINIT treatment of perturbation (respfn) should NOT be requested in order to use Optic, but with the present ordering of the help files and tutorial, this is not obvious. In a future version, the tutorials and help files will be reorder and modified.
It will be easier to discover the present file with the help of the tutorial (lesson_optic).
It is worthwhile to print this help file, for ease of reading.
Optic allows to compute the frequency dependent linear optical dielectric function and second order nonlinear optical susceptibility. An introduction to such computations is given in the following paper :
The specific purpose of the Optic utility is to read in the position matrix elements
generated by ABINIT (also giving the momentum matrix elements), and then use Eq. 46 in
Ref. 1
to determine the
linear and Eqs. 49, 50 and 51 in Ref. 1 to determine the nonlinear
optical response of the material under investigation.
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The use of Optic is quite simple :
optic < optic.files > optic.logwhere the optic.files file contains three information : the name of the input file, the name of an output file (actually unused), and the root name for all other output files. These input files will be described in the next section.
However, before being able to use Optic, you must have obtained, from the main abinit program, four different files, corresponding to the physical system that you want to study:
The main abinit program has the capability to compute derivatives of wavefunctions with respect to their wavevector. This is explained in the ABINIT (respfn) help file. Such a calculation implies treating three d/dk perturbations, with numbers 3*natom+1, 3*natom+2 and 3*natom+3 (that is, for a unit cell with 2 atoms, perturbations number 7, 8 and 9). In the 2-atom case, the associated files needed for Optic have the index _1WF7 , _1WF8 , and _1WF9 .
The formalism implemented in Optic treats explicitly the eigenstates lying in the range of energy between the lowest occupied wavefunction and the highest one plus the maximal excitation energy (chosen by the user). All the other ones are neglected. This has two important consequences for the preliminary runs :
A typical optic.files file is presented below :
optic.in ! Name of input file optic.out ! Unused optic ! Root name for all files that will be producedPlease note that the format of input files for Optic has changed from Abinit v8.0 Since very few input parameters are required for Optic, the optic.in file contains them with the namelist format. The order of the three parts, namely FILES, PARAMETERS and COMPUTATIONS must be kept unaltered.
&FILES ddkfile_1 = 'toptic_1o_DS4_1WF7', ddkfile_2 = 'toptic_1o_DS5_1WF8', ddkfile_3 = 'toptic_1o_DS6_1WF9', wfkfile = 'toptic_1o_DS3_WFK' / &PARAMETERS broadening = 0.002, domega = 0.0003, maxomega = 0.3, scissor = 0.000, tolerance = 0.002 / &COMPUTATIONS num_lin_comp = 1, lin_comp = 11, num_nonlin_comp = 2, nonlin_comp = 123,222, /
The list of input variables for the optic input file is presented in the topics Optic.
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Name: case_a_b-linopt.out
Contains the following 3 data sets
Name: case_a_b_c-ChiKIND1.out
KIND1:This can be TotIm, TotRe or TotAbs
Contains: column 1 - energy(eV), column 2 and 3 - imaginary (KIND1=TotIm),
real (KIND1=TotRe) or absolute (KIND1=TotAbs) value of the abc component of
the nonlinear optical susceptibility. Second column contains values in
electro-static units (esu) and third column contains values in the SI units.
Name: case_a_b_c-ChiKIND2.out
KIND2:This can be Im, Re or abs
Contains: column 1 - energy(eV), column 2, 3 inter and column 4, 5 intra band
contributions to the imaginary (KIND2=Im), real (KIND2=Re) or absolute
(KIND2=Abs) value of the abc component of the nonlinear optical susceptibility.
These components are labeled as inter and intra in Eqs. 49-51 in Ref. 1.
All the values are in electro-static units (esu). In the header of all the
above files you can find information about the calculation.
Some results of nonlinear optical spectrum for
GaAs(LiF???) are presented in this document to show what can be expected.
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1) All I get is zeros in my *-linopt.out file. Why?
There are several possibilities.
Let us explore some of them here:
2) All I get is zeros in my *-ChiKIND.out file. Why?
Two most common mistakes are: