Dear researchers,
Here is my input file:
# avogadro generated ORCA input file
# Basic Mode
#
! RHF SP def2-SVP Opt Freq MORead
#! BP RI OPT FREQ def2-SVP def2/J MORead
%moinp "co2.gbw"
* xyz 0 1
C -5.20115 2.99851 0.00000
O -6.37575 3.02514 0.00000
O -4.02656 2.97165 0.00000
*
I haven't found any mention of this error anywhere.
Thanks
This is a common error associated with linear molecules (fragments). Judging by your message, Orca requires that the linear fragment be oriented along the Z axis. That is, the coordinates should look like this:
C 0. 0. 0.
O 0. 0. 1.5
O 0. 0. -1.5
Alexey N. Masliy Thank you very much!
But now, if I may, I would like to know how this can be done. I tried to make the alignment along the z axis in Avogadro, but I can't get it to work so that Orca accepts it
For example,
I get this:
* xyz 0 1
O 0.00000 -0.00000 -1.13697
C 0.00000 0.00000 0.00000
O -0.00009 0.00009 1.13698
*
or this:
* xyz 0 1
O 0.00009 -0.00009 2.27395
C 0.00000 -0.00000 1.13698
O 0.00000 0.00000 0.00000
*
and it doesn't suit
The problem with the CO2 molecule and other similar particles containing linear fragments is that when translated into internal coordinates, the computer faces the problem of orientation relative to atoms lying on the same straight line. To avoid this in the case of CO2, you can add a pseudoatom (XX) to the linear fragment so that it does not lie on this straight line. For example,
From 0. 0. 0.
XX 0. 1. 0.
O 0. 0. 1.5
O 0. 0. -1.5
In more complex particles, you just need to make sure that three atoms lying on the same straight line never follow each other.
Alexey N. Masliy
I'm not sure if I understand, but I'll try to do something and add this pseudoatom.
Thank you very much!
All quantum chemical software packages use redundant coordinates to improve the convergence procedure. The program constructs a coordinate system line by line, and if the initial data is specified in the form of Cartesian coordinates, the redundant coordinates are constructed on the basis of three consecutive previously defined atoms, and if these atoms lie on the same straight line, then a problem arises with constructing the plane. Therefore, such situations should always be avoided. That is, there should not be a situation where three atoms in a row lie on the same straight line.
Alexey N. Masliy Thanks to you, things started to work out for me! I added a dummy atom. And at least twice the calculations went through without errors. True, the spectrum turned out to be completely different from the real one. I tried to recalculate again, but, despite the fact that the dummy atom was in place, I started getting the same error again. I'm going to count it all over again. And I hope it works this time!
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