This part of the guide discusses the prediction of Infrared (IR) and Raman spectra with CRYSTAL, using Cu2O as an example.

Prerequisites

You will need the data from harmonic frequency calculation at the Γ-point for Cu2O.

Additional information

It is also possible to calculate the IR and Raman spectra simultaneously with the harmonic frequencies. But especially if you are working on hypothetical materials that have not yet been characterized experimentally or where the crystal structure has uncertainities, it makes sense to calculate the harmonic frequencies first. This way, you won't waste time on spectral calculations for systems which are not true local minima.

If you want to calculate the IR and Raman spectra together simultaneously with the harmonic frequencies, you can use the input below without the RESTART keyword.

Input for IR and Raman spectra

You need to be in the directory that contains the output from the harmonic frequency calculation (all files starting with Cu2O_Pn-3m_PBE0_TZVP_fq).

Save the harmonic frequency calculation output:

cp Cu2O_Pn-3m_PBE0_TZVP_fq.o Cu2O_Pn-3m_PBE0_TZVP_fq.o.fqonly

Edit the input file of the harmonic frequency calculation (Cu2O_Pn-3m_PBE0_TZVP_fq.d12):

The FREQCALC block needs a number of modifications:

Cu2O_Pn-3m_PBE0_TZVP_fq.d12
FREQCALC
RESTART
NUMDERIV
2
INTENS
INTRAMAN
INTCPHF
ENDINTCPHF
IRSPEC
DAMPFAC
8
ENDIRSPEC
RAMANEXP
298.15 632.8
RAMSPEC
DAMPFAC
8
VOIGT
0.5
ENDRAMSPEC
ENDFREQ

Line 2 contains new keyword RESTART. This keyword reads the data from the harmonic frequency calculation from the file Cu2O_Pn-3m_PBE0_TZVP_fq.freqinfo. Without this keyword, the harmonic frequencies will be recalculated.

INTENS keyword requests the calculation of IR intensities.

INTRAMAN requests the calculation of Raman intensities.

INTCPHF requests the calculation of IR and Raman intensities with analytical CPHF/CPKS-scheme. This is required for Raman intensities.

IRSPEC requests a plot of IR spectrum. DAMPFAC is the Full Width at Half Maximum (FWHM) of the spectrum in cm–1. By default, the IR spectrum is produced using Lorenzian broadening.

RAMSPEC requests a plot of Raman spectrum. DAMPFAC is the FWHM of the spectrum in cm–1. The setting VOIGT 0.5 requests pseudo-Voigt broadening (50:50 Lorenzian:Gaussian).

RAMANEXP is optional, it includes the temperature (K) and laser wavelength (nm) used during the experimental determination of the Raman spectrum. If you have these available, it is recommended to use them to improve the agreement with the experimental intensities. 

Complete input for the calculation

Here is the complete input for the calculation: 

Cu2O_Pn-3m_PBE0_TZVP_fq.d12
Cu2O (Pn-3m) IR and Raman spectrum (DFT-PBE0/TZVP)
CRYSTAL
0 0 0
224
4.31764698
2
29 0.00 0.00 0.00
8  0.25 0.25 0.25
FREQCALC
RESTART
NUMDERIV
2
INTENS
INTRAMAN
INTCPHF
ENDINTCPHF
IRSPEC
DAMPFAC
8
ENDIRSPEC
RAMANEXP
298.15 632.8
RAMSPEC
DAMPFAC
8
VOIGT
0.5
ENDRAMSPEC
ENDFREQ
ENDGEOM
8 7
0 0 6 2.0 1.0
  27032.382631      0.21726302465E-03
  4052.3871392      0.16838662199E-02
  922.32722710      0.87395616265E-02
  261.24070989      0.35239968808E-01
  85.354641351      0.11153519115
  31.035035245      0.25588953961
0 0 2 2.0 1.0
  12.271113873      0.39768730901
  4.9159842006      0.24627849430
0 0 1 0.0 1.0
 0.90086482370      1.0000000000
0 1 1 0.0 1.0
 0.25000000000      1.0 1.0
0 2 4 4.0 1.0
  75.300554155      0.60685103418E-02
  17.743733858      0.41912575824E-01
  5.5355828651      0.16153841088
  2.0685535103      0.35706951311
0 2 1 0.0 1.0
 0.78238772422      1.0000000000
0 3 1 0.0 1.0
 1.2000000000       1.0000000000
29 12
0 0 8 2.0 1.0
 377518.79923      0.22811766128E-03
 56589.984311      0.17688035931E-02
 12878.711706      0.91993460227E-02
 3645.3752143      0.37411016434E-01
 1187.0072945      0.12189873737
 426.46421902      0.28983900714
 165.70660164      0.41531872174
 65.598942707      0.21905799287
0 0 4 2.0 1.0
  414.41265811     -0.24682525053E-01
  128.32056039     -0.11716827406
  20.622089750      0.55301315941
  8.7821226045      0.52242718609
0 0 2 2.0 1.0
 13.741372006      -0.22736061821
 2.2431246833      0.71761210873
0 0 1 1.0 1.0
 0.89370549079     1.0000000000
0 0 1 0.0 1.0
  0.35              1.0000000000
0 1 1 0.0 1.0
  0.14              1.0 1.0
0 2 6 6.0 1.0
 2034.7596692       0.23524822298E-02
 481.90468106      0.19134070751E-01
 154.67482963      0.90171105278E-01
 57.740576969      0.26063284735
 23.099052811      0.42093485770
 9.3882478591      0.24344615121
0 2 3 6.0 1.0
 37.596171210      -0.28991094530E-01
 5.1240690810      0.54919083831
 2.0119996085      0.93793330488
0 2 1 0.0 1.0
 0.73860686002     1.0000000000
0 3 4 10.0 1.0
 74.129460637      0.14363216676E-01
 21.359842587      0.86628177096E-01
 7.4995240537      0.25631430541
 2.7601394169      0.40374062368
0 3 1 0.0 1.0
 0.95362061236     0.39427042447
0 3 1 0.0 1.0
 0.28420862520     0.23091146816
99 0
ENDBAS
DFT
PBE0
ENDDFT
SHRINK
0 8
8 8 8
TOLINTEG
8 8 8 8 16
TOLDEE
9
MAXCYCLE
100
FMIXING
80
EXCHSIZE
30000000
BIPOSIZE
30000000
END

Running the job

Submit the job normally using jsub:

jsub -np 8 crystal Cu2O_Pn-3m_PBE0_TZVP_fq.d12

Analyzing the results

An example output is available here: Cu2O_Pn-3m_PBE0_TZVP_fq.o.

You can use CRYSPLOT or Jmol to visualize the results (see Aalto Solid State Chemistry Wiki).


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