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20

ORCA The local pair-natural orbital (DLPNO) based coupled cluster method have been managed to investigate large organic molecule and small proteins (linear C150H302 (452 atoms, >8800 basis functions) , Crambin with 644 atoms, and more than 6400 basis functions ,C350H902 (>1000 atoms, > 20000 basis functions)). Riplinger, C., Sandhoefer, B., Hansen, ...


13

There was a bug with the PModel guess of iodine, which leads to a very poor initial guess for molecules containing iodine, and consequently divergent SCF calculation. This bug has been fixed in ORCA 5.0. ORCA 5.0 can be downloaded at https://orcaforum.kofo.mpg.de/app.php/dlext/?cat=13. Note that ORCA 5.0 does not support the keywords Grid5 and FinalGrid5 ...


13

Incidentally, I initiated some discussions along these lines in these questions for HF-DFT (also called 'density-corrected' DFT) here, and here. I'm familiar with Quantum ESPRESSO, so I can detail a procedure with QE. If you want to generate a Hartree-Fock density, you can just turn on a hybrid functional (say HSE06) and turn up the fraction of exact ...


11

Note that the DLPNO method is only implemented in ORCA. There are indeed analogous and similarly efficient and accurate methods, the PNO-LCCSD method in Molpro [doi.org/10.1021/acs.jctc.7b00799] and the LNO-CCSD method in MRCC [doi.org/10.1021/acs.jctc.9b00511]. To my knowledge exact analytical gradients are not implemented for either of them. There is an ...


10

I’ll expand on this later but here is the abbreviated version. CTF The CTF code can do very large iterative CCSD and CCSDT using a dense spin-orbital formalism. CCSD up to 55 (50) water molecules with cc-pVDZ http://solomonik.cs.illinois.edu/talks/molssi-monterey-may-2017.pdf The 8-water CCSDT problem in Table 3 took 15 minutes on 1024 nodes of BG/Q and ...


10

Electrostaic embedding is usually on the QM-side as simple point charges which add to the total hamiltonian of the nuceli+electrons. It should be just a simple coulumb interaction. Any modern electronic structure calculation software should support aleast electrostatic embedding. Openmolcas, Orca, Dalton/LSDalton, Bagel all support electrostatic embedding, ...


9

tldr: This is something of an eternal debate. IMHO very small imaginary frequencies can be okay, but it depends on your system and needs. As you might see from the various comments above, there are often different opinions on whether very small imaginary frequencies matter. The truth is, that it depends a bit on the size of the molecule and what you plan to ...


8

This second dipole moment is almost surely the excited state. You can see the nuclear contributions are identical and the rotational constants are also the same. This means they are both calculations of the same geometry. You can also see the magnitude of the dipole moment increases in the second calculation. This is very common in excited states. The ...


8

I figured out the correct formatting. The section defining the QM needs to have the MORead option, the %moinp section, and the %scf section. Example: !B3LYP 6-31G* Slowconv MOREAD *xyz 0 3 ... * %moinp "01.ethylene.gbw" %scf rotate {7, 8, 90, 0, 0} end end


7

Localized natural orbitals methods allow tackling huge system sizes; some links were already given above. Of course, the accuracy remains sometimes a question in such methods: the methods rely on thresholds, which may not have always been converged! So you should keep in mind that these are not black-box tools like conventional coupled-cluster theory. The ...


7

To tether a set of atoms (index or fragment) in pDynamo, the below lines are needed (energy model can vary): tethers = pM.SoftConstraintContainer () system.DefineSoftConstraints ( tethers ) reference = Clone ( system.coordinates3 ) tetherEnergyModel = SoftConstraintEnergyModelHarmonic ( 0.1 , 500.0 ) NAME1 = "IronOH" sele1 = ...


7

As far as I know, analytic gradients for DLPNO-CCSD are not available in ORCA. Analytic first derivatives are available for both closed-shell and high-spin open-shell cases, which could be used for computing other first-order properties. As the first exercise to implement analytic gradients within the DLPNO setup, the DLPNO-MP2 method was considered and the ...


6

vkj's answer addressed the third part of the question. I'll answer the first part. Which quantum chemistry methods can be used in an external electrostatic field? Also which software supports that? I'm interested in anything from semiempirical (eg XTB) to DFT (eg ωB97, B3LYP-D3) to coupled cluster (eg DLPNO-CCSD(T)). The only starting point I have is a few ...


6

First of all, if you are only interested in molecules with about the same size as the ones in the article you cited, then TDDFT is probably not the best method for this purpose. ORCA supports many methods that are much more reliable than TDDFT for singlet-triplet gaps, yet are still affordable for molecules of this size, for example DLPNO-STEOM-CCSD, NEVPT2, ...


6

From the ORCA forum thread: Actually there is an undocumented feature for this purpose: %scf efield X-field-strength-in-a.u. , Y-field-strength-in-a.u. , Z-field-strength-in-a.u. end I have used it to compare dipole moments obtained via numeric and analytic differentiation and it worked fine. But do be careful as undocumented features do not officially ...


6

All files are always created in the run directory where ORCA runs. I specifically did not want to deal with environment variables and path names and all that. Hope that helps! best wishes, Frank Neese


6

I think Nike has answered to all questions adequately enough. I am sharing my understanding as one of the developers of the PNO-based local coupled-cluster (CC) methods, codes for computing response properties in particular. In coupled-cluster theory, the correlated wavefunction is described in terms of "cluster amplitudes" (which are the ...


6

I'll answer each of your three questions separately, but the one you say is "most important" will go first 😊 And most importantly, why are they used for correlation calculation? They can significantly reduce the cost of a calculation on a big system, especially when there is a large number of "virtual" orbitals (unoccupied orbitals) in ...


5

In pdynamo 3.0.9 A vector3 can be defined by importing from Geometry module. For example, center = Vector3.Null ( ) It looks like a vector3 is just 3 element vector. Not really sure but here is what I found in pScientific/Symmetry/PointGroupFinder.py file You will need to get the center of mass however by looping over each atom in the geometry e.g. $...


4

So this question is related to the recent discussion in Procedure to classify errors in Kohn-Sham DFT where I already gave the general procedure: get the density from some level of theory, and use it to run a single-point DFT calculation. This question was about how to do this in Q-Chem; it's actually quite simple. Here's an example input for a calculation ...


4

MRCC MRCC stores 1- and 2-electron integrals in an ASCII file called fort.55 which is formatted very similarly to FCIDUMP. The fort.55 file stores the integral values and integral indices in exactly the same way as in FCIDUMP, but has a different header. One has to delete the header of the FCIDUMP file and replace it with something like this (here my example ...


3

GAMESS(US) has this facility implemented, but this feature may not be available in the public release.


3

I found the most consistent way to localize orbitals. Use the orca_loc extension. You must create and input file where define the localization method (PM, Boys, ...), and the orbitals you want to localize. To run it: orca_loc name.inp -i


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