Questions tagged [orca]
For questions about (or involving) the ORCA electronic-structure package.
109 questions
8 votes
1 answer
401 views
When doing a CASSCF calculation, why do we rotate by 90 degrees rather than by a different amount?
This question pertains on how to do CASSCF calculations in ORCA: Why do we specifically rotate by 90 degrees when we swap MOs to create our orbital space? Thanks
- 631
6 votes
1 answer
141 views
Studying weak interactions in PySCF
I am trying to reproduce an Energy Decomposition Analysis within the PySCF framework and compare the results with Orca. The problem is that while my script shows good agreement for systems such as C₂H₆...
- 63
10 votes
1 answer
104 views
Why does the ORCA tutorial use the optimized ground state geometry rather than the optimized S1 excited state geometry, for the fluorescence spectrum?
In the ORCA tutorial, in the part that talks about the simulation of fluorescence spectrum of benzene (6.18.2. Fluorescence Rates and Spectrum), the optimized ground state geometry was used in the ...
- 631
5 votes
0 answers
67 views
Broken symmetry calculation to estimate magnetic coupling parameter J
I would like to estimate the magnetic coupling parameter J, and I was confused about which geometry should be used for the calculations. Should I be using the structure that corresponds to the high-...
- 631
7 votes
1 answer
240 views
NMR calculations using RI-MP2 in ORCA
I have been trying to do some NMR calculations for Zinc-BINAP-complexes that can benefit from GIAO (gauge-including atomic orbital) for 31P shieldings. I have read that GIAO is the go-to method for ...
- 665
6 votes
0 answers
83 views
What method do you recommend for an organic molecule with 6 unpaired electrons?
I am using ORCA. What computational method (e.g., DFT flavor) would you recommend me to investigate which spin state is lower in energy? Thanks.
- 631
6 votes
1 answer
137 views
Obtain HF canonical in ORCA using RIJCOSX
The title says it all. I would like to obtain canonical orbitals in ORCA when using RIJCOSX (or other approximate RI techniques). When I write the MOs via ...
- 163
4 votes
1 answer
127 views
Difficulty getting ORCA Software to run in parallel
I am new to ORCA and attempting to run a job using parallel CPUs on a server. The program keeps crashing with the following error message: ...
- 41
1 vote
0 answers
38 views
Energy values are abruptly changing from gas phase calculations to solvent (acetonitrile)phase. how to solve this problem in DFT calculations
For reaction modeling study of cobalt catalyzed [3+2} cycloaddition reaction between alkyne and cyclohexenone derivatives; The energy differences between the intermediates and transition states are ...
- 11
6 votes
2 answers
122 views
How Can I Escape Saddle Points in Excited-State Geometry Optimizations (Orca)
I’m encountering a recurring issue in excited-state geometry optimizations (e.g., S₁, T₁, T₂), where even after converging with very tight settings like VeryTightOpt, I still find one or more ...
- 662
4 votes
1 answer
134 views
ORCA version 4.2.1 basis set
I'm trying to run single point energy on Os octahedral complex I dont know what is wrong with my basis set I'm trying to get method that is similar to genecp 6311G* CHN and SDD for Os this my inout ...
- 41
4 votes
1 answer
122 views
How to change Gaussian Z-Matrix to ORCA internal coordinates?
I am trying to perform geometry scans (is that what you call it) for different molecules in ORCA 6.0.1. I did the typical thing of defining a parameter using: ...
- 665
6 votes
1 answer
158 views
Why double hybrid functionals produce different results in different packages?
I'm calculating the single-point energy of the Nitrogen dimer using a double-hybrid functional called "mPW2PLYP". This is a widely known double hybrid functional available for use in ...
- 311
7 votes
1 answer
120 views
How to find the symmetry unique atoms of a molecule with a specified point group by any software or tool?
Suppose, for cyclopropane, the highest point group is D3h. However, I want to define it to its subgroup C2v for my NwChem calculation. But for specifying a different point group NwChem requires the ...
- 71
2 votes
1 answer
166 views
Conversion of Gromacs topology to amber or ORCA
Is there any clean way to convert gromacs topology file to amber prmtop file or orca forcefield file? I have .gro and .top file from gromacs MD Simulation and now I would like to perform QM/MM geo-opt ...
- 21