Unanswered Questions
496 questions with no upvoted or accepted answers
7
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Interstitial sites: edge and face sharing?
In close packed structures there is one octahedral hole per close packed atom. In a HCP unit cell these octahedra form a chain of face sharing polyhedra. Is this this universal in close packing or ...
- 963
7
votes
1
answer
3k
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Beer's law: UV-Vis absorbance values exceeding 2
In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity.
As general rule of thumb neither high, nor very low absorbance are used for ...
- 29.2k
7
votes
1
answer
4k
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Geometry of AsF5 molecule
Which of the following is the best description of the arragement of fluorine atoms around the arsenic atom in a molecule of $\ce{AsF5}$?
(a) trigonal bipyramid
(b) octahedron
(c) tetrahedron
(...
- 38.4k
6
votes
0
answers
78
views
Why SCF-MO methods fail when treating bond-breaking processes?
I'm currently studying the EVB(Empirical Valence Bond) approach. While reading on this article (https://pubs.acs.org/doi/10.1021/ja00224a011), the author mentioned about the usage of SCF-MO formalism ...
- 221
6
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103
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Obtaining transition density matrix
I'm trying to assemble a transition density matrix on quantum computer using one-body excitation $\widehat{E}$ operator on 2 active spatial orbitals, i.e. on 4 spin-orbitals. The problem is, I need to ...
- 4,606
6
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71
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Are there examples of publications using DFT instead of HF as a coupled-cluster reference?
I have been searching for a while, and only managed to find an article by M. Saitow,[1] where CAM-B3LYP orbitals are used. I was wondering if this has been done elsewhere.
It was recommended to me by ...
- 44.3k
6
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0
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201
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Why are the unsaturated fatty acids usually unconjugated?
My textbook gives the structures of the unsaturated fatty acids in food including oleic acid, linoleic acid, linolenic acid and docosatetraenoic acid. I figure that when two or more $\ce{C=C}$ double ...
- 38.4k
6
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192
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Hund's rule for comparing term symbol energies in excited state
This question was asked in an exam:
The lowest energy electronic state for excited state carbon atom is,
a. $^1D_2$
b. $^3D_1$
c. $^3D_3$
d. $^3D_2$
Although we have been taught Hund's rule for ...
- 7,030
6
votes
0
answers
357
views
Geometry of a free radical at the bridgehead carbon
With reference to J. Am. Chem. Soc. 1968, 90 (19), 5266–5267, they state:
The most favorable geometry of aliphatic free radicals remains an unsolved problem, since existing data are consistent with a ...
- 7,030
6
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0
answers
114
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Solving the Schrödinger equation for a rotating triatomic linear molecule
This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles.
For dipoles, the total ...
- 647
6
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0
answers
109
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Why does BCF (boron carbofluoride) not exist?
$\ce{BCF}$ (boron carbofluoride, or carbon borofluoride, not to be confused with another so-called BCF molecule that has nothing to do with it) should exist as a vapor molecule with the bonds $\ce{B≡C-...
- 61
6
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0
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90
views
How long would it take for a tank of same-spin hydrogen atoms to become a tank of H₂?
In the question
Is there an energy cost associated with flipping the spin of an electron?, it is shown that it is very unlikely for two hydrogen atoms to bond if their electrons have the same spin. ...
- 2,242
6
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0
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573
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How to extract force constants for normal modes from ORCA?
I am following the computational method described in Scientific Reports.[1] Where the authors analyze the contribution of each excited state normal-modes to the shift of the transition energy. For ...
- 44.3k
6
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0
answers
383
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How to evaluate the expectation value of the Hamiltonian for a three electron Slater determinant?
I'm having trouble with a few concepts dealing with slater determinants and many electron systems. In particular, when dealing with 3 electron systems, I know that
$$
\psi_0 = \frac{1}{\sqrt{6}} \det
...
- 11.8k
6
votes
0
answers
201
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Vibrational Self-Consistent Field
There are a few things about VSCF that I don't understand:
Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode ...
- 11.8k