23 votes
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Do we know for sure that all atomic and molecular wavefunctions decay exponentially as r goes to infinity?

I'll answer this question from the theoretical side. The exponential behavior follows simply from the Schrödinger equation. Consider the one-electron Schrödinger equation: $$ (-\frac{1}{2}\nabla^2 + V(...
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12 votes

Plotting of natural bond orbitals (NBOs)

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, ...
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12 votes
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Gaussian-type orbitals vs Slater-type orbitals in terms of computational efficiency

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 ...
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11 votes

How to calculate and plot localised orbitals with xTB?

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 ...
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11 votes

Is there any relation between static correlation and finite-temperature smearing?

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 ...
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What is the difference between orbital localisation and NBO?

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 ...
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How to interpret molden AO/MO coefficients?

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 ...
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10 votes

Plotting of natural bond orbitals (NBOs)

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 ...
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9 votes
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How do I interpret the Gaussian16 wavefunction file?

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 ...
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9 votes

Plotting of natural bond orbitals (NBOs)

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 ...
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How to calculate/plot molecular orbitals with XTB?

I think the --molden flag should give you a molden file with the orbitals.
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8 votes
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What is the difference between orbital localisation and NBO?

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. ...
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8 votes
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How are molecular orbitals constructed from the coefficients and basis set?

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 ...
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Is the number of basis functions same in the different atoms in the 6-31G basis set?

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 ...
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Critical difference and roles of Slater- and Gaussian-type orbitals

"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 ...
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Orthonormality of Kohn-Sham orbitals

You are correct that orbitals from different $k$-points should be orthogonal. $k$-points are irreps of the translation group and, similar to the irreps of point groups for molecules, integrals of two ...
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Molecular orbitals and active space

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 ...
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8 votes

How to calculate molecular orbitals of octaoxygen under high pressure?

TL;DR Two recently published and easy-to-use methods come to mind: X-HCFF (1) GOSTSHYP (2) Both are available in Q-Chem 5 (6). The user can simply input a desired pressure, and the algorithms take ...
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The number of orbitals in Gaussian/GAMESS log file

As Nike mentioned, most basis sets produce more orbitals than the minimal set that you tend to think of for these elements. We can see how this works out for 6-31G(d,p) by looking at how the basis set ...
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7 votes

The number of orbitals in Gaussian/GAMESS log file

Yes, a good basis set will contain virtual (unoccupied) orbitals, in addition to the orbitals that are occupied by electrons. Almost always: the larger the basis set, the more accurate the ...
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Is the number of basis functions same in the different atoms in the 6-31G basis set?

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 ...
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6 votes

Critical difference and roles of Slater- and Gaussian-type orbitals

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 ...
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How can I implement the Cartesian harmonics?

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. ...
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6 votes

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

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
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6 votes

Plotting of natural bond orbitals (NBOs)

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-...
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Does the INIWAV tag in VASP assume that the wavefunctions are plane waves?

No, it randomly chooses the different plane-wave coefficients $c_{Gbk}$ for wavevector $G$, of each trial Kohn-Sham state at each band $b$ and k-point $k$, $\psi_{bk}(r)=\sum_G c_{gbk}e^{iG.r}$. The ...
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Modify ORCA orbitals for CASSCF

You can use the "rotate" keyword in the SCF block, like %scf rotate {30,27,90} (38,41,90} {39,48,90} end end The "90"s mean "90 degrees&...
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6 votes

Too large value of s-orbital in near nucleus

Individual basis functions do not have to be physical. Only the superposition of basis functions is used to represent atomic or molecular orbitals. Several kinds of atomic basis functions can be used, ...
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4 votes

The number of orbitals in Gaussian/GAMESS log file

I should complement Nike and Tyberius' answers by the simple statement that e.g. hydrogen only consists of a single S function for the non-interacting atom. When the atomic symmetry is lifted, you get ...
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Is there any relation between static correlation and finite-temperature smearing?

You may like to read this 2012 JCP paper to know TAO-DFT: https://aip.scitation.org/doi/10.1063/1.3703894 Even with the exact exchange-correlation energy functional in KS-DFT, one still needs to ...
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