[Pw_forum] about raman?

[Eduardo Ariel Menendez Proupin]

Neither do I know if the values are correct, it depends on the units, and
very details.  You should  search for experimental values of Raman cross
sections in ZnO and compare with yur numbers.

However, it is crucial to know what is printed at the output.
Regarding the units, in dynmat.f90 I can read
 !   Raman cross sections are in units of bohr^4/(Ry mass unit)
write (6,'(5x,"Raman cross sections are in A^4/amu units")').
I guess A means Angstrom, but I am not sure that the comment and the write
statement are consisten. Also,  I think that  cross section should have
units of area. In any case, it is quite common to report Raman cross
sections in "arbitrary units" due to experimental difficulties to precisely
determine them.

please, see PRB 54, 7830 (1996) and take a look at dynmat.f90 to see exactly
what is printed on the column Raman. It corresponds to a particular
configuration of incoming and outgoing polarisations and scattering
direction.
Pay attentio to this part of dynmat.f90

       alpha = (raman(1,1,nu) + raman(2,2,nu) + raman(3,3,nu))/3.d0
       beta2 = ( (raman(1,1,nu) - raman(2,2,nu))**2 + &
                 (raman(1,1,nu) - raman(3,3,nu))**2 + &
                 (raman(2,2,nu) - raman(3,3,nu))**2 + 6.d0 * &
          (raman(1,2,nu)**2 + raman(1,3,nu)**2 + raman(2,3,nu)**2) )/2.d0
       write (6,'(i5,f10.2,2f10.4,f15.4,f10.4)') &
            nu, freq, freq*cm1thz, infrared(nu), &
            (45.d0*alpha**2 + 7.0d0*beta2)*r1fac, &
             3.d0*beta2/(45.d0*alpha**2 + 4.0d0*beta2)

(45.d0*alpha**2 + 7.0d0*beta2)*r1fac is what is written on column "Raman"

Good luck


-- 


Eduardo Menendez Proupin
Departamento de Química Fisica Aplicada
Facultad de Ciencias
Universidad Autónoma de Madrid
Phone: +34 91 497 6706

On leave from: Departamento de Fisica, Facultad de Ciencias, Universidad de
Chile URL: http://fisica.ciencias.uchile.cl/~emenendez

"*Padece, espera y trabaja para gentes que nunca conocerá y que a su vez
padecerán, esperarán y trabajarán para otros, que tampoco serán felices,
pues el hombre ansía siempre una felicidad situada más allá de la porción
que le es otorgada. Pero la grandeza del hombre está precisamente en querer
mejorar lo que es. En imponerse Tareas. En el Reino de los Cielos no hay
grandeza que conquistar, puesto que allá todo es jerarquía establecida,
incógnita despejada, existir sin término, imposibilidad de sacrificio,
reposo y deleite. Por ello, agobiado de penas y de Tareas, hermoso dentro de
su miseria, capaz de amar en medio de las plagas, el hombre puede hallar su
grandeza, su máxima medida en el Reino de este Mundo*".
Alejo Carpentier, El reino de este mundo, (1949).

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