Hybrid RI-DFT and aoforce

[antti_karttunen]

What is the state of the hybrid RI-DFT analytic 2nd derivative implementation in TURBOMOLE 5.9? I made some tests using RI-B3LYP and aoforce happily accepts the B3LYP functional in combination with RI. No warnings are given, except the usual note about RI implementation of aoforce being in preliminary state. However, the results do not look so good. Here are the wavenumbers (cm-1) for the three IR-active vibrations of T_d-symmetric P₄:

B3LYP      RI-B3LYP    RI-B3LYP 
analytic   analytic    numeric
367.23     420.13      367.68
460.56     506.59      460.14
602.77     628.66      602.37

As can be seen, the analytic RI-B3LYP wavenumbers are very different from traditional B3LYP and numeric RI-B3LYP values. This difference then affects the zero-point energies and thermodynamical quantities. The non-RI and RI geometries are nearly identical, as are the relative energies when compared to for example P₈. The similar comparison for pure functional (BP86) yielded the expected results (almost identical wavenumbers for RI and non-RI).

So should I just avoid calculating the RI-hydrid-DFT frequencies analytically?

[uwe]

Hi,

you are right - aoforce does not check for the combination of RI and a hybrid functional !!

Hence: PLEASE do not do RI-hybrid-functional calculations with aoforce.

But it should be sufficient to remove the $ridft and/or $rij keyword from the control file, which will cause aoforce to perform a usual non-RI calculation. The results should be almost identical to the non-RI calculation. And if you want, you could do a single point energy calculation without RI first...

Regards,

Uwe

[klem]

Have been calculations for RI-hybrid-functional using aoforce implemented properly in the newest version of Turbomole (6.5) or it still give bad results?

[uwe]

Hi,

that was a bug in an old Turbomole version in 2007 and it has been fixed in 2007. Version 5.9 was buggy and this has been fixed in 5.9.1.

Uwe