[CP2K-user] [CP2K:16401] what is the unit for IR intensity using normal mode analysis in cp2k?

[Fangyong Yan]

Dear Professor Hutter and your group members,

I checked the source code, and found IR intensity is equal to
SQRT(DOT_PRODUCT(D_deriv,
D_deriv)). Based on Darling and Schlegel's paper, the IR intensity is
proportional to (d(mu)/dQ)^2. So does it mean the IR intensity should
be DOT_PRODUCT(D_deriv,
D_deriv), not SQRT(DOT_PRODUCT(D_deriv, D_deriv))? (Is this a mistake??)

Here I attach Darling and Schlegel's paper.

The source code is vibrational_analysis.F,

                  IF (calc_intens) THEN

                     D_deriv = 0._dp

                     DO j = 1, nvib

                        D_deriv(:) = D_deriv(:) + dip_deriv(:, j)*Hint2(j,
i)

                     END DO

                     intensities(i) = SQRT(DOT_PRODUCT(D_deriv, D_deriv))

                  END IF

Thanks ahead for your help, and Merry Christmas!!

Fangyong

On Tue, Dec 21, 2021 at 5:19 PM fyya... at gmail.com <fyyan2019 at gmail.com>
wrote:

> Hi, all,
>
> What is the unit for IR intensity using normal mode analysis in cp2k? The
> IR intensity is proportional to d(mu) / dQ, d(mu) is the change of the
> dipole moment, and dQ is the change of normal mode coordinate Q.
>
> There are prefactor for the exact IR intensity,  see eq. 8 in Cynthia L.
> Darling and H. Bernhard Schlegel, J. Phys. Chem. 1994, 98, 5855-5861.
>
> So what is the equation for calculating the IR intensity in cp2k, is there
> a reference for it? Once we know the equation, we can know the unit.
>
> Thanks!
>
> Fangyong
>
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