25 votes
Accepted

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(...
wzkchem5's user avatar
  • 9,621
19 votes
Accepted

Why is my hydrogen energy not equal to -0.5 hartrees?

Yes, the exact orbital energy of the hydrogen atom is $-1/2\ E_h$. The problems in the calculation are as follows. First, you are running ROKS. ROKS has many definitions in the literature; PySCF ...
Susi Lehtola's user avatar
  • 19.1k
15 votes
Accepted

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 ...
I have no free time anymore's user avatar
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, ...
I have no free time anymore's user avatar
12 votes

Why is my hydrogen energy not equal to -0.5 hartrees?

The exact non-relativistic ground state electronic energy of a hydrogen-like atom, assuming that the nucleus is "clamped", point-sized, and with an infinitely large mass compared to the mass ...
I have no free time anymore's user avatar
11 votes
Accepted

How to calculate/plot molecular orbitals with XTB?

I think the --molden flag should give you a molden file with the orbitals.
Kexanone's user avatar
  • 523
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 ...
Phil Hasnip's user avatar
  • 7,187
11 votes

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 ...
Martin - マーチン's user avatar
10 votes
Accepted

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 ...
Susi Lehtola's user avatar
  • 19.1k
10 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 ...
S R Maiti's user avatar
  • 6,841
10 votes
Accepted

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 ...
Susi Lehtola's user avatar
  • 19.1k
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 ...
Fedor Goumans's user avatar
9 votes
Accepted

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. ...
jheindel's user avatar
  • 3,534
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 ...
Felix's user avatar
  • 1,421
9 votes
Accepted

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 ...
Tyberius's user avatar
  • 15.5k
9 votes
Accepted

How is the zero energy defined for molecular orbitals?

The zero point of orbital energies is usually defined as the vacuum level, i.e. the energy of a hypothetical orbital that is infinitely diffuse and does not come close to any nuclei or other electron. ...
wzkchem5's user avatar
  • 9,621
8 votes
Accepted

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 ...
I have no free time anymore's user avatar
8 votes
Accepted

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 ...
Tyberius's user avatar
  • 15.5k
8 votes
Accepted

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 ...
I have no free time anymore's user avatar
8 votes
Accepted

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 ...
I have no free time anymore's user avatar
8 votes
Accepted

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 ...
Tyberius's user avatar
  • 15.5k
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 ...
Yoda's user avatar
  • 180
7 votes
Accepted

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&...
wzkchem5's user avatar
  • 9,621
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 ...
I have no free time anymore's user avatar
7 votes
Accepted

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, ...
Susi Lehtola's user avatar
  • 19.1k
7 votes

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 ...
S R Maiti's user avatar
  • 6,841
7 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 ...
Susi Lehtola's user avatar
  • 19.1k
7 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
FrankNeese's user avatar
6 votes
Accepted

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. ...
Susi Lehtola's user avatar
  • 19.1k
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-...
Camps's user avatar
  • 23.3k

Only top scored, non community-wiki answers of a minimum length are eligible