Questions tagged [quantum-chemistry]
357 questions
57
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3 answers
Are there exact analytical solutions to the electronic states of the hydrogen molecular ion $\mathrm H_2^+$?
The hydrogen molecular ion (a.k.a. dihydrogen cation) $\mathrm H_2^+$ is the simplest possible molecular system, and as such you'd hope to be able to make some leeway in solving it, but it turns out that it's much harder than you'd hope. As it turns…
Emilio Pisanty
- 137,480
28
votes
2 answers
Is there experimental verification of the s, p, d, f orbital shapes?
Have there been any experiments performed (or proposed) to prove that the shapes of the s,p,d,f orbitals correspond to our spatial reality as opposed to just being a figment of the mathematics that give us something to visualize?
user263399
- 1,144
26
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3 answers
What is the quantum mechanical explanation of the octet rule?
What is the quantum mechanical explanation of the octet rule? In other words, what makes the octet rule be true from a quantum mechanical view? How we explain what makes some atoms don't follow the octet rule using QM?
Hakim
- 1,031
22
votes
2 answers
Why does the conjugated $\pi$ bond not violate the Pauli Exclusion Principle?
Let's look at the molecule 1,3 butadiene:
$CH_2=CH-CH=CH_2$
and number the carbon atoms 1 to 4 from left to right.
The bonds between 1 and 2 and between 3 and 4 are double bonds: each constitutes a $σ_{2p}$ and a $π$ bond (molecular orbitals).…
Gert
- 35,561
21
votes
1 answer
Why does Hartree-Fock work so well?
Why does the Hartree-Fock method for electronic structure work so well for atoms?
More specifically, why is the "correlation energy" a relatively small component of an atom's (ground state) energy?
I might also ask why electron-electron interaction…
creillyucla
- 1,009
20
votes
3 answers
Are orbitals observable physical quantities in a many-electron setting?
Orbitals, both in their atomic and molecular incarnations, are immensely useful tools for analysing and understanding the electronic structure of atoms and molecules, and they provide the basis for a large part of chemistry and in particular of…
Emilio Pisanty
- 137,480
19
votes
4 answers
1D Infinite Square Well: Box Suddenly Increases in Size. How treat this?
I am currently working my way through John S. Townsend book "A Fundamental Approach to Modern Physics" (ISBN: 978-1-891389-62-7). Exercise 3.12 (p.111) is about the 1D infinite square well. The box has the potential barriers at $x=0$ and…
Yoda
- 639
19
votes
6 answers
Does there exist a free good molecule / atom simulation software?
I'm looking for a software or software package (for example C/C++) that can simulate a lot (say thousands at least) of molecules in action (ie. in movement or attached to say static walls).
I have found several but they seems to be either 'gas…
Valmond
- 193
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16
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2 answers
Why is the distinction between Mott Insulators and Charge Transfer Insulators important?
Strongly-correlated metals often become insulators due to the repulsive Coulomb interaction, and the basic model here is the Mott-Hubbard…
KF Gauss
- 8,314
16
votes
2 answers
Why does iteratively solving the Hartree-Fock equations result in convergence?
[ Cross-posted to the Computational Science Stack Exchange: https://scicomp.stackexchange.com/questions/1297/why-does-iteratively-solving-the-hartree-fock-equations-result-in-convergence ]
In the Hartree-Fock self-consistent field method of solving…
James Womack
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15
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3 answers
Chemical reaction as state transition?
When considering diffusion of chemicals, the reaction part is business of chemical kinetics, where the relevant characteristics of different substances come from collision theory together with some classical statistics. If one want to go deep down,…
Nikolaj-K
- 8,873
15
votes
4 answers
Why do covalent bonds form?
why in a covalent bond are "the bonded electrons are in a lower energy state than if the individual atoms held them at the same proximity"?
Also is it correct that " I think when you start pushing two molecules together orbitals between the two…
15
votes
2 answers
Does the $p^+p^-e^-$ system have bound states?
This is batted a bit off the wall, so bear with me. The hydrogen molecular ion, $\mathrm{H}_2^+$, is the simplest three-body system in molecular physics, and in the Born-Oppenheimer approximation its electronic Schrödinger equation is separable…
Emilio Pisanty
- 137,480
13
votes
1 answer
Does the hydrogen anion have bound excited states?
I'm having some trouble puzzling out the literature regarding the existence of bound excited states in the hydrogen anion, H$^-$.
Wikipedia claims that no such states exist, and that the subject is uncontroversial, stating that
H$^−$ is unusual…
Emilio Pisanty
- 137,480
11
votes
2 answers
Why does Hartree-Fock (HF) theory even work?
Let’s say we have $N$ electrons and we want to derive the Hartree-Fock (HF) equations. The first step would be to define a Slater determinant of $N$ electrons:
$$\psi(x_1,x_2,… x_N) = \frac{1}{\sqrt{N!}}\begin{vmatrix}\phi_{1}(x_1) & \phi_{2}(x_1)…
Lockhart
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