Hello water! Your first ORCA calculation

Our first calculation will be the energy of a water molecule, using Hartree-Fock theory and the DEF2-SVP basis. All you need to run ORCA is an input text file, such as this water.inp:

!HF DEF2-SVP
* xyz 0 1
O   0.0000   0.0000   0.0626
H  -0.7920   0.0000  -0.4973
H   0.7920   0.0000  -0.4973
*

Note

The input usually has the .inp extension, but .txt is also ok.

We strongly recommend to create a new folder for any calculation. In this case we will create our input file in a new directory called firstcalc and navigate to it.

Linux/Mac:

mkdir ~/firstcalc
cd ~/firstcalc

Windows:

mkdir C:\firstcalc
cd C:\firstcalc

(To find the Windows prompt, click windows key and type "prompt".)

You can now run ORCA. First, make sure that it is installed correctly and the system path is set (see Assigning PATH variables).

orca water.inp

The output is then printed on the screen.

Save output to a file

To save the output in a text file water.out instead, use the > operator (on both Linux/Mac and Windows):

orca water.inp > water.out

You can then open the file to see the output (make sure not to overwrite it while the calculation is running). More on the input and output analysis next.

Note

You don't need to worry about the other programs in the installation folder for now, ORCA will take care of calling the right one when needed.