Questions tagged [orca]

For questions about (or involving) the ORCA electronic-structure package.

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8
votes
0answers
60 views

Using “soft” constraints / bias in geometry optimization?

I study molecules weakly bound to nanoclusters and surfaces. During geometry optimization, I often run into problems like for example a small metal cluster behave nicely and has a given, stable ...
10
votes
2answers
291 views

How to calculate DFT energy with density from another level of theory?

I need to calculate the DFT energy given the density of another level of theory, for example Hartree Fock. $E[\rho_{HF}]$ This is sometimes used to fix various electron delocalization errors in ...
8
votes
1answer
95 views

How to get the .47 file from ORCA for natural bonding orbital analysis

I am trying to perform NBO analysis with relaxed density matrix with the open-source program JANPA. I am following the guide here. The first step is to get the NBO input .47 file from Orca v4.2.1. The ...
8
votes
2answers
175 views

What are Pair Natural Orbitals?

Recently, I came across electron correlation methods that use local pair natural orbitals (LPNOs) or domain-based local pair natural orbitals (DLPNO), such as DLPNO-MP2, DLPNO-CCSD etc. The dynamic ...
15
votes
1answer
168 views

Is it right to neglect very small imaginary frequencies?

I'm running a DFT optimization (B3LYP/def2-TZVP) and frequencies in ORCA for a molecule. And I get one or two very small (1-6 cm^-1) imaginary frequencies which corresponds to a slight bend of the ...
7
votes
1answer
75 views

Adding external electric field in ORCA with specific strength

Can anybody share methods to apply an external Electric field in ORCA? thanks!
11
votes
1answer
163 views

How do you calculate the change in dipole moment from ground to first excited state using ORCA?

How do you calculate the change in dipole moment from the ground to first excited state using ORCA? I have done DFT to get the dipole moment at the ground state and TDDFT of this neutral molecule. How ...
10
votes
2answers
304 views

Analytic gradient for DLPNO-CCSD

Is there a formula for analytical gradients (for geometry optimization) for the DLPNO-CCSD method? I ask because I know that it is not implemented in ORCA. Maybe PNO-CCSD is implemented in MRCC or ...
11
votes
0answers
106 views

I ran TDDFT on some small molecules. For some files, the ORCA output files cut short and contain no absorption data. What could be the reason? [closed]

Below is just the end of the output file, and the top of the input file. This is for the molecule FDICTF. The calculation did not run out of time. I ran a batch of 15 molecules, all with same ...
5
votes
2answers
60 views

For software that does not support FCIDUMP format, what format is used and how can we get the software to interact with FCIDUMP integrals?

Complementary to this question: How do the various programs read or write integrals in FCIDUMP format? which attempts to list all electronic structure packages that support the ...
4
votes
1answer
39 views

Defining coordinates using Vector3

I am trying to implement a tether restraint in the MM region of my QM/MM calculation using pDynamo (CHARMM/ORCA interface). I need to define the origin as a Vector3. Does anyone know how to do this?
10
votes
1answer
65 views

Constraining a set of atoms in the MM region using pDynamo (CHARMM/ORCA interface)

I am trying to perform a QM/MM optimization in which my substrate is in the MM region. However when this happens there are significant changes to the geometry (undesired). I want to avoid fixing all ...
7
votes
1answer
50 views

How to localize orbitals in pDynamo (CHARMM/ORCA interface)?

Does anyone know how to localize orbitals in pDynamo (CHARMM/ORCA interface). I am trying to identify the correct orbitals to swap for my high-spin iron(IV) system.
9
votes
1answer
62 views

How to swap orbitals in ORCA?

I am trying to swap orbitals for a high-spin iron(IV) complex. The orbitals that correspond to the iron are not in any of the SOMOs. I am using the pDynamo QM/MM program, which is an interface for ...
20
votes
3answers
221 views

What is the largest system that has been studied by the coupled cluster method?

This is parallel to the analogous question about the largest DFT calculation: What is the largest material that has been studied using density functional theory? I assume we allow high performance ...