Molcas Forum

daishudaishu

Member

Registered: 2019-02-24

Posts: 22

RASSI related issues

Dear all,
I am new to MOLCAS and I have a few questions regarding RASSI.

1. What is the difference between Dipole transition strengths and Velocity transition strengths? It seems that Velocity transition strengths have more transitions. I also have the following problematic transitions. How to fix them?

  Problematic transitions have been found

      From   To      Difference (%)  Osc. st. (len.) Osc. st. (vel.)
      --------------------------------------------------------------

         1    3       2.92597307E+03  1.46543431E-01  4.84285311E-03
         1    4       6.64231197E+04  6.27576361E-01  9.43395865E-04
         1    5       4.08509395E+03  1.44468430E-01  3.45197579E-03
         1    6       6.59642641E+03  7.52411350E-02  1.12360131E-03
         1    7       1.41504350E+04  2.65485367E-01  1.86299833E-03
         1    8      ---------------  2.01091635E-04 below threshold
         1    9       1.34571652E+04  4.44563085E-01  3.27917435E-03
         2    3       1.37303374E+04  4.23237366E-01  3.06020999E-03
         2    4      ---------------  2.47198162E-02 below threshold
         2    5       3.56528607E+03  1.33771083E-01  3.64967647E-03
         2    6       2.87207377E+03  1.54981881E-01  5.21460411E-03
         2    7       5.10917270E+04  5.04321757E-02  9.85162617E-05
         2    8       2.27836827E+03  8.15141215E-02  3.42731285E-03
         2    9      ---------------  2.19976874E-04 below threshold
         3    4       4.95839688E+02  9.07561761E-02  1.52316433E-02
         3    5      ---------------  1.60522986E-05 below threshold
         3    6       6.82272198E+02  3.23120546E-02  4.13053854E-03
         3    7       4.23012077E+01  9.57746159E-03  1.65990677E-02
         3    8       8.56758686E+01  4.80407247E-04  3.35383160E-03
         3    9       4.61267377E+03  9.73984568E-02  2.06673454E-03
         4    6       2.39252672E+04  9.61169655E-02  4.00066167E-04
         4    7       5.14254381E+04  1.87236892E-01  3.63387288E-04
         4    8       4.56142612E+02  1.66418042E-03  2.99236272E-04
         4    9       2.76523806E+05  7.00452100E-01  2.53214686E-04
         5    6      --------------- below threshold  4.28296115E-04
         5    7      --------------- below threshold  6.64989546E-05
         5    8       3.14596762E+03  1.08354473E-01  3.33812550E-03
         5    9       3.26249615E+03  1.06134937E-01  3.15643298E-03
         6    7       9.83345104E+01  1.27437767E-04  7.65166999E-03
         6    8       3.37041344E+03  1.32935788E-01  3.83054614E-03
         6    9       3.12175866E+03  4.96575605E-02  1.54131845E-03
         7    8       2.03694151E+01  2.95438578E-04  3.71011438E-04
         7    9       1.34914021E+03  7.19291017E-02  4.96357091E-03

2. How to plot the absorption spectrum from RASSI result?
I write a code to read the following data and the '++ Dipole transition strengths ' part. I plot the absorption spectrum with the energy from 'Rel lowest level' column and the 'osc. strength' column from '++ Dipole transition strengths'? Is it the right way to do it?

  SPIN-FREE ENERGIES:
  (Shifted by EVAC (a.u.) =      -7159.9652382578)

 SF State       Relative EVAC(au)   Rel lowest level(eV)    D:o, cm**(-1)

     1             0.0000000000        0.0000000000              0.0000
     2             0.3705486971       10.0831436364          81326.0387
     3             9.1885937463      250.0343714112        2016663.2253
     4             9.5913129239      260.9929184108        2105049.8683
     5            11.2925771979      307.2866772929        2478434.2177
     6            11.3194018559      308.0166134171        2484321.5497
     7            11.4983300401      312.8854973053        2523591.7469
     8            20.4662626953      556.9153745885        4491825.4606
     9            20.8399783665      567.0846959789        4573846.5697

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,012

Re: RASSI related issues

Dipole (should be "length") and velocity oscillator strengths are two different approximations to compute oscillator strengths, see e.g. https://doi.org/10.1002/qua.560010304. The length version seems to be more commonly, but there's indication that the velocity one tends to be more accurate. "Problematic" transitions are just those for which length and velocity give significantly different results, you may be able to reduce the different by enlarging the basis set.

As for the spectrum, yes, you take the energy difference between states and the oscillator strength (length or velocity). Or you can maybe use https://github.com/MGDelcey/PlotCAS

daishudaishu

Member

Registered: 2019-02-24

Posts: 22

Re: RASSI related issues

Thanks a lot!