Questions tagged [quantum-chemistry]

Quantum chemistry is a subfield of quantum mechanics. Like its parent field, quantum chemistry focuses on understanding physical phenomena occuring at the atomic scale. Quantum chemistry however is more focused on providing useful descriptions of electronic structure to aid in understanding chemical problems (e.g. reactions, spectra, dynamics, ...).

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20
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1answer
463 views

Is it possible to compute the colour of *any* molecule?

Above are some spectral emission lines for hydrogen, helium and neon. Using the Schroedinger equation, it's possible to derive the colours that hydrogen will emit when light is fired at it. A little ...
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2answers
2k views

Bonding and anti-bonding orbitals in the light of time-dependent Schrödinger equation?

In organic chemistry, people draw 2p orbitals like this: and then they explain how the orbitals combine to non-bonding (π*) or bonding (π) molecular orbitals, like this: depending on whether the ...
8
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1answer
791 views

Intrinsic Reaction Coordinate - What does 'Connectivity' really mean?

I am currently in the process of connecting transition state (TS) structures to other minima in order to determine a reaction pathway. Now I understand the basic concepts of this method. You start ...
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3answers
4k views

Why are these molecular orbitals invalid for hexatriene?

Here are the MOs (more accurately, the breakdown of the MOs) for conjugated hexatriene: Now, when first asked to draw the MOs myself, I drew this one for $\psi_3$: It still has two nodes, and is ...
15
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2answers
4k views

Why are there quantised energy levels in the vibrational energy of a molecule?

Why are the energy levels for vibrational energy in a molecule discrete as opposed to continuous? I don't understand how a vibration can't have continuous amounts of energy that depend on the ...
10
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3answers
10k views

Why can an s orbital only hold two electrons?

According to Pauli’s exclusion principle, an $s$ orbital contains at most two electrons with the opposite spin (up and down). Why can't an $s$ orbital contain a third electron whose state is the ...
11
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1answer
466 views

Negative Kelvin Temperature

I remember my Physical Chemistry Professor saying that very tiny negative Kelvin temperatures have been achieved on the quantum level. Is this true?
9
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3answers
1k views

Can quantum entanglement affect the chemistry of molecules?

I recently heard a talk from a physicist about experiments on simple two-atom molecules in vacuum that showed that certain behaviour of the molecules was explained by quantum entanglement. Now this ...
15
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1answer
956 views

Naming of quantum chemistry basis sets

For some DFT calculations I performed with localized (Gaussian) basis sets, I wonder how the basis sets I used are properly named. The names I could gather are: H, C and O: 6-311G(d,p) Al: 8-511G* ...
5
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2answers
261 views

Energy of the n-th level for an atom

Going through the Bohr's model and his assumptions, I came across with this formula to find the energy of the n-th level of any atom: $$E = - \frac{Z k_e e^2}{2r_n} = -\frac{Z^2(k_e e^2)^2m_e}{2\...
5
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1answer
459 views

Does this set of quantum numbers have a unique solution?

I received the following question: Complete the missing values for the four quantum numbers: $n=?$, $\ell = 2 , m_\ell = 0$ , $m_s= ? $ . The problem is that I think $n$ can be any number ...
7
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1answer
225 views

What is the 'ancestral term' in the LS coupling scheme?

On the physics.nist.gov site: http://physics.nist.gov/Pubs/AtSpec/node06.html The table titled "Atomic structural hierarchy in LS coupling and names for the groups of all transitions between ...
9
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438 views

multielectron spin-orbit coupling and energy level

For multi-electron atoms for which the Hamiltonian (including the spin-orbit coupling) reads $$H=\sum_i T_i-Z\sum_i V_i+\sum_i V_i^{\text{s.o.}}+\sum_{i>j}V_{ij}$$ The $T_i$ are the kinetic ...
4
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1answer
3k views

Moment of inertia for a triatomic molecule

What does the moment of inertia for a molecule mean? How is it useful? Most importantly, how would I go about solving it for a triatomic molecule?
5
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1answer
200 views

Modeling perturbations of a quantum mechanical system

I'm wondering how to properly perturb a quantum mechanical system. I'm looking for a way to express the return to equilibrium of such a perturbed state, where the perturbation is in the Hamiltonian. ...
21
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1answer
456 views

Is the Springborg 6D phase space model used in modern molecular orbital modeling?

In a series of papers in the early 1980s, Michael Springborg explored an interpretation of the Wigner phase space function as an electron density in a six-dimensional $(q,p)$ phase space. He applied ...
9
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1answer
106 views

Has QTPIE ever been applied to 1D metals such as polyacetylene?

QTPIE is a fluctuating charge model that substantially improves modeling of polarization and charge transfer. I was curious whether it has ever been applied to 1D metals such as polyacetylene to ...
32
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3answers
2k views

Pauli exclusion principle and resonance

I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance. This seems to disobey Pauli's exclusion ...
23
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3answers
1k views

Symmetry lost in orbitals?

I've always thought that orbitals lead to a loss of symmetry, and have never been able to give myself a satisfactory answer to this. I'll explain via an example: Let's take an $\ce{N^3+}$ atom. It's ...
21
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3answers
743 views

Non-integer hybridization

I've known that hybridization in distorted geometries is not exactly $sp^3$ or $sp^2$ or whatever. For example, $\ce{PH3}$ has nearly pure $p$ orbitals in the $\ce{P-H}$ bond, and the lone pair is in ...
78
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7answers
113k views

Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?

My chemistry book explains that even though electrons in the $\mathrm{2p}$ orbital are closer to the nucleus on average, electrons from the $\mathrm{2s}$ orbital spend a very short time very close to ...

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