Need more information.

Input file and last 10-20 lines from output file.

its better to create your input file using Avagadro, this error occurs if your input file is wrong.

Abhishek Katoch When i create an input file using avagadro, it does not have the basis sets that i need to run the calculation.

H. M. N. P. Gunarathna in the same input file replace the the existing basis set and try to replace the one you wish to use, if still error occurs, you need to install latest version or install some files. or check this file .cpp in the existing orca folder.

Abhishek Katoch I need to geometry optimization using DFT B3LYP cc-pVQZ basis set of a selected molecule and need to know the energies of MOs (HOMO LUMO). Lets say ethanol for an example. If it is okay could you please let me know the input code for it?

I tried replace the basis set as you said and istalled the latest version. But the problem is same. I think my input code is wrong.

! B3LYP cc-pVQZ opt

! KDIIS DAMP SOSCF LSHIFT rijcosx

* xyz 0 1

C -0.570184 -0.027415 0.061066

H -1.059981 -0.677797 0.786241

H -1.071556 -0.118316 -0.902852

C 0.899274 -0.433274 -0.083437

H 0.956453 -1.466772 -0.426156

H 1.406977 -0.350205 0.878788

H 1.395391 0.209840 -0.812005

O -0.657301 1.137419 0.447493

H -1.299076 1.726520 0.050861

*

But I must say right away that the B3LYP functional incorrectly estimates the LUMO energies.

Yes, and the basis set for LUMO is needed with the addition of diffusion functions.

H. M. N. P. Gunarathna Try using cc-pVDZ or aug-cc-pVDZ.

For now, pplease folllow

https://www.scribd.com/document/429791150/ORCA-JumpStartGuide-4-1#

i cant help now, since i am out of place.