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Your supervisor is correct that in almost all practical cases in quantum chemistry, the cost savings of using Gaussian-type orbitals far outweigh the disadvantages of needing more orbitals. First of all, there is a bit of a misconception that Slater-type orbitals are far more accurate. The motivation for using Slater-type orbitals is due to their resemblance ...


11

You can do it with Multiwfn (http://sobereva.com/multiwfn/) First, xTB has to be run with the --molden directive, to output the converged molecular orbitals as a molden file. Normally xTB will produce this file with the name molden.input. Multiwfn is able to open this file. After opening, select option 19 for Orbital Localization Analysis. You can change ...


11

NBO 7.0 The program NBO 7.0 seems to be quite well maintained, with version 7.0.9 released fewer than 30 days ago. Advantages: Has interfaces to ADF, DEMON2K, FIREFLY/PC-GAMESS, GAMESS(US), GAUSSIAN, JAGUAR/SCHROEDINGER, MOLCAS, MOLPRO, NWChem, ORCA, PQS, Psi4, QChem, SPARTAN, TeraChem, TURBOMOLE. At least 2 new releases were issued already in 2020, and at ...


10

This is a nice thought, but the two are not actually related. In principle, static correlation is completely accounted for in the exchange-correlation functional of Kohn-Sham DFT and there is no need for any mixing of the Kohn-Sham states, in fact it would lead to an incorrect result. In practice, the exchange-correlation functional is approximated and so ...


10

Note: This was a response I've originally written on Chemistry Stack Exchange, so it was intended to be very brief. Natural Bond Orbital Theory is basically (among plenty of other uses) providing an orbital localisation scheme to achieve similarity to Lewis structures. In some of my answers you have probably read the term 'Lewis-like' structures for these ...


10

Okay, so there are many layers to this question. cc-pVTZ for H is [5s2p1d/3s], which comes out to 3 + 2*3 + 5 = 3+6+5 = 14 basis functions per atom, which are composed of 16 primitives (the contracted s function). Now, while there are 1 and 3 cartesians for the s and p shells, for the d shell you have 6 cartesian functions but only 5 spherical functions. ...


9

ADF With the Amsterdam Modeling Suite you can calculate (ADF, DFTB) and plot NBOs in the graphical user interface within the same package. Here's an example applied to NMR analysis. Here's one applied to TDDFT UV/VIS, including NTOs and NBOs. Here's one on NBO and other analysis / visualization (QTAIM) You are welcome to have a Free Trial!


9

Q-Chem + Jmol The combination of Q-Chem and Jmol seems to work well (but is not yet well documented). Q-Chem In the Q-Chem input file one has to put $rem ... nbo = 1 $end $nbo PLOT $end This calls the NBO program and writes out the information of interest to the files $QCSCRATCH/FILE.[31-39] NBO The content of the files written is FILE.31 Basis set ...


9

I think the --molden flag should give you a molden file with the orbitals.


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I have yet to find a source that lays this out explicitly, but from the examples I could find, it is not too hard to infer the meaning of these sections. To start with (and possibly point you in the right direction to look for more information), this type of *.wfn file was developed as the input format for AIMPAC and quickly spread to be used as an output ...


8

As you said above, nitrogen has 2 s orbitals and one p orbital. However, one would typically freeze the chemically inactive 1s orbital, leaving you 5 electrons in 4 orbitals per atom, or 10 electrons in 8 orbitals for N$_2$; this is denoted $(10e,8o)$. Going beyond the minimal STO-3G basis, in addition to the occupied molecular orbitals (which are poorly ...


8

Yes you're absolutely correct that the basis sets for O and C will typically have the same number of orbitals (not just for the 6-31G basis set but also for the famous cc-pVXZ family, and other basis sets). It's true that O has more electrons than C, but in both cases, the electrons are primarily occupied in the $1s$, $2s$, and $2p$ orbitals. If you're ...


8

Things are more clear to me when I look at the basis set in CFOUR format, because of the information at the top which tells me how many primitives and how many contractions there are for each type of orbital: O:MIDI Huzinaga MIDI 2 0 1 3 2 6 3 281.86658 42.416000 9.0956200 11.46603 0.887860 0.278800 0.069060 0.000000 0.00000000 0.393159 0.000000 0....


7

In short, natural atomic orbitals are the orbitals you get from diagonalizing the one-particle reduced density matrix. One can then localize this set of orbitals via some maximization criteria. Natural bond orbitals are the orbitals you get when maximizing the occupancy of orbitals such that electrons occupy the space between two atoms or on a single atom. ...


7

"My question is that, does the GTO simply represent the STO by using many Gaussians, or not?" There does exist the STO-nG basis set family in which $n$ Gaussian orbitals are fitting to represent a single STO. These are never used for serious applications to predict spectroscopic, thermodynamical, or kinetic properties of molecules (or atoms) ...


6

I think that it is a feature of how the basis set is defined. 6-31G is a valence double-zeta basis set of the Pople family. Here, 6 means that the core orbitals are represented with 6 Gaussian functions (GTO) while 31 means the valence orbitals are split into two orbitals with the scheme 3 GTO + 1 GTO. So, I looked at the basis set data for 6-31G, and it ...


6

The question is not very well-posed. However, the question appears to be about whether rotational invariance is honored by LCAO calculations. The old-time approach is to use Cartesian basis functions. Translating our origin to the nucleus, we can write the Cartesian basis functions in the form $\psi({\bf r}) = N x^k y^l z^m \exp(-\alpha r^2)$, where $\lambda:...


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


5

It's important to also note that the STO-nG family is a Gaussian fit to an old, minimal STO basis. Larger STO basis sets ranging up to quadruple-zeta quality are included in e.g. the ADF program that is based on Slater-type orbital basis sets. As Nike already said, more reasonable GTO basis sets don't even try to imitate STO basis sets, but rather just aim ...


5

Jmol Jmol is a free, open source viewer of molecular structures useful for students, educators and researchers in chemistry, biochemistry and other fields dealing with molecular structure. It is cross-platform, running on Windows, Mac OS X, and Linux/Unix systems. The Jmol application is a standalone Java application that runs on the desktop. The JSmol is ...


3

MOPAC MOPAC (Molecular Orbital PACkage) is a semiempirical quantum chemistry program based on Dewar and Thiel's NDDO approximation. If you qualify for Academic not-for-profit use, request your password here. Using the keyword local, you can calculate the localized orbitals are also known as Natural Bond Orbitals or NBO.


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