Re: Using wavefunction yielded by Gaussian as initial guess of ORCA

dummy@example.com (saeed_E) — Sun, 27 Sep 2020 16:55:51 +0000

Dear Tian,
Too many thanks for such very nice, valuable, and highly informative comments.

Sincerely yours,
Saeed

Using wavefunction yielded by Gaussian as initial guess of ORCA

dummy@example.com (sobereva) — Sun, 27 Sep 2020 12:38:12 +0000

Here I describe how to use Multiwfn to transfer converged wavefunction yielded by Gaussian as initial guess of ORCA. This trick must be useful for many ORCA users.

1 Run a normal Gaussian task along with "int=NoBasisTransform" keyword, and meantime explicitly specify %chk to retain the .chk file.

2 Use formchk of Gaussian to convert .chk to .fch or .fchk

3 Load .fch/fchk into Multiwfn, enter main function 100, select subfunction 2, then select option 9 and input "y" to export current wavefunction to .mkl file.

4 Assume that the mkl file is test.mkl, then use this command to convert it to test.gbw file: orca_2mkl test -gbw

5 Now you can specify moread keyword in ORCA input file, and add %moinp "test.gbw" to use the wavefunction in test.gbw as initial guess.

HINT: A much more convenient way is using the shell script "chk2gbw.sh" in "examples/scripts" folder of Multiwfn binary package. Assume that there are A.chk, B.chk and C.chk in current folder, simply run this script, it will convert all the .chk to .gbw files with same name (A.gbw, B.gbw and C.gbw), and meantime the accompanied ORCA input files (A.inp, B.inp and C.inp) will be yielded. After simply replacing the keywords in the .inp files with the ones you actually need, you can start ORCA calculations.

Similarly, wavefunction given by ORCA can also be used in Gaussian calculation as initial guess. The simplest way is using the examples/scripts/gbw2chk.sh script in Multiwfn package, it will convert all .gbw files in current folder to .chk files, which can then be employed as initial guessing wavefunction by using guess=read keyword in Gaussian. (NOTE: Please use Multiwfn updated on 2021-Oct-1 or later if the wavefunction comes from UHF/UKS calculation, otherwise beta orbitals cannot be loaded by Gaussian via guess=read).

Notice that in order to use the above two scripts, Gaussian, ORCA and Multiwfn must have been installed on your machine, more specifically, the formchk, orca_2mkl and Multiwfn commands can be directly used without inputting their absolute paths. If you do not know how to correctly install Multiwfn, see Section 2.1.2 of Multiwfn manual.

More detailed information with a practical example is given in my blog article: //www.umsyar.com/517 (written in Chinese).