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I am looking for a way to convert XYZ coordinates into z-matrix for Gaussian input files. I need to specify certain coordinates in the matrix, therefore, the automatic built-in function from gaussview isn't of much help. Do you know of a program that can help me? Thanks in advance for your help!

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    $\begingroup$ molden can write z-matrices, you can load in a xyz file and save it as z-matrix $\endgroup$ – Fl.pf. Jun 14 '17 at 13:14
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    $\begingroup$ Chemcraft has a very descent built-in constructor of Z-matrices. $\endgroup$ – Wildcat Jun 14 '17 at 14:56
  • $\begingroup$ +1 for chemcraft. you can define the coordinates you need and even let the software do the rest. $\endgroup$ – DSVA Jun 14 '17 at 22:48
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Try Open Babel, the windows GUI has a lot of features that may be of help depending on what are those specifics you need in your Z-matrix.

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As mentioned in the comment by Fl.pf, the program molden has a very powerful ZMAT Editor:

  • You can hand pick the atoms that define bond lengths, angles and dihedrals
  • You can save as: GamessUS, GamessUK, Gaussian z-mat, mopac, xyz

If you want to convert back to xyz with obabel (for example after replacing a variable in the zmat with a range of values), use mopac (mopin in obabel).

Molden takes a bit to get used to, but this task can be done quite well there.

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Avogadro, nice, clean and very user friendly. Just draw the molecule, then navigate to menu Extensions → Gaussian. Here you can format and select z-matrix for Gaussian input.

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Gaussian provides all you need to do this with the newzmat program. It literally does all this, no need for 3rd party software.

I found it works best to put the Cartesian coordinates in a file by themselves and save it as xyz, then in the command line just run (Note the atom types need to be in front of the coordinates so

i.e. C XXXX YYYYY ZZZZZ would be one line in the file if your first atom was carbon)

newzmat -ixyz name_of_xyz_file

It will output name_of_xyz_file.com in z-matrix format.

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