## Calculation of refractive indices

Command line: `abrefr`
```***** Program  abrefr  (version October 1996) - c Petr Mikulik *****
***** Copying policy: GNU General Public License               *****
***** See http://www.sci.muni.cz/~mikulik/ for more details    *****
Usage: abrefr    ... calculate refr. indices
abrefr -b ... calculate Bragg angles
abrefr -a ... calculate interplanar angles

* Choose crystal system: *
Cubic       Tetragonal  Orthorombic  Hexagonal
Monoclinic  tRigonal    trIclinic:   c
Enter lattice parameters (Angstroms, degrees):
a = 5.43
Volume of the elementary cell = 160.103 A^3

Known wavelengths [A]:
TiKa1=2.74851    CrKa1=2.28962    FeKa1=1.93597    CoKa1=1.78896
CuKa2=1.54439    CuKa=1.54184    CuKa1=1.54056    CuKb1=1.39222
MoKa2=0.71359    MoKa=0.711445   MoKa1=0.7093     MoKb1=0.632288
AgKa2=0.563798   AgKa=0.561603   AgKa1=0.559408   AgKb2=0.497069
TaKa1=0.215947   WKa1=0.20901    AuKa1=0.180195
Choose wavelength (string and/or value [A]): 1.54

Atom (element): Si
look: atomic scatt. factor = Z = 14
atomic mass              = 28.086
dispersion correction    = (0.244,0.33)
Number of this atom in the cell: 8

Atom (element) [type . to end]:

Wavelength:     1.54 A

Elementary cell:
sum of atomic scatt. factors  = 112
sum of dispersion corrections = (1.952,2.64)
electron density [1/A^3]      = 0.6995496
total relative mass           = 224.688
density [g/cm^3]              = 2.330432
=> structure factor     = (113.952,2.64)
=> susceptibility 0     = (-1.514068e-05,-3.507740e-07)
=> 1 - refractive_index = (7.570341e-06,1.753870e-07)
=> critical angle       = 0.2229 deg
Results saved in file abrefr.dat
```

## Calculation of Bragg angles

Command line: `abrefr -b`
```***** Program  abrefr  (version October 1996) - c Petr Mikulik *****
***** Copying policy: GNU General Public License               *****
***** See http://www.sci.muni.cz/~mikulik/ for more details    *****
Usage: abrefr    ... calculate refr. indices
abrefr -b ... calculate Bragg angles
abrefr -a ... calculate interplanar angles

* Choose crystal system: *
Cubic       Tetragonal  Orthorombic  Hexagonal
Monoclinic  tRigonal    trIclinic:   C
Enter lattice parameters (Angstroms, degrees):
a = 5.43
Volume of the elementary cell = 160.103 A^3

Known wavelengths [A]:
TiKa1=2.74851    CrKa1=2.28962    FeKa1=1.93597    CoKa1=1.78896
CuKa2=1.54439    CuKa=1.54184    CuKa1=1.54056    CuKb1=1.39222
MoKa2=0.71359    MoKa=0.711445   MoKa1=0.7093     MoKb1=0.632288
AgKa2=0.563798   AgKa=0.561603   AgKa1=0.559408   AgKb2=0.497069
TaKa1=0.215947   WKa1=0.20901    AuKa1=0.180195
Choose wavelength (string and/or value [A]): 1.54
Remark: this calculates only the Bragg angle, not the extinction rules.
H K L = 1 1 1
Bragg angle=14.2181 deg
inter-planar distance Dhkl=3.13501 A
*** type X to exit, otherwise continue: g
H K L = 2 2 2
Bragg angle=29.4212 deg
inter-planar distance Dhkl=1.56751 A
*** type X to exit, otherwise continue: g
H K L = 0 0 4
Bragg angle=34.5565 deg
inter-planar distance Dhkl=1.3575 A
*** type X to exit, otherwise continue: x
```

## Calculation of interplanar angles

Command line: `abrefr -a`
```***** Program  abrefr  (version October 1996) - c Petr Mikulik *****
***** Copying policy: GNU General Public License               *****
***** See http://www.sci.muni.cz/~mikulik/ for more details    *****
Usage: abrefr    ... calculate refr. indices
abrefr -b ... calculate Bragg angles
abrefr -a ... calculate interplanar angles

* Choose crystal system: *
Cubic       Tetragonal  Orthorombic  Hexagonal
Monoclinic  tRigonal    trIclinic:   T
Enter lattice parameters (Angstroms, degrees):
a = 5.2
c = 6.1
Volume of the elementary cell = 164.944 A^3

===================================================
1 ... change plane (H1 K1 L1) = (0 0 1)
2 ... change plane (H2 K2 L2) = (1 0 0)
=> angle between them = 90 deg
P ... set precision=5
X ... exit
New indices: 1 1 1

===================================================
1 ... change plane (H1 K1 L1) = (0 0 1)
2 ... change plane (H2 K2 L2) = (1 1 1)
=> angle between them = 58.919 deg
P ... set precision=5
X ... exit
New indices: 0 1 1

===================================================
1 ... change plane (H1 K1 L1) = (0 1 1)
2 ... change plane (H2 K2 L2) = (1 1 1)
=> angle between them = 37.272 deg
P ... set precision=5
X ... exit