The quantum-chemistry tag has no wiki summary.
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The Molecular Hamiltonian and the avoidance of Overcounting
Whenever I see the total non-relativistic molecular Hamiltonian,
$\hat{H}_{molecular} = \hat{T}_{e} + \hat{T}_{n} + \hat{V}_{ee} + \hat{V}_{nn} + \hat{V}_{en}$
I always notice that the sums ...
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1answer
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Coulomb interaction and conservation laws
In many-body solid-state physics, the Coulomb interaction term in the Hamiltonian usually implies the momentum conservation law in indicies:
$$H_c=\frac{1}{2} \sum_{\mathbf{k},\mathbf{k}',\mathbf{q} ...
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76 views
Ground state energy of hydrogen molecule ion
In this paper, it is mentioned:
Furthermore, since the
energy of $H_2^+$in the ground state must be lower than that of an
H atom in the ground state,the negative (attractive) forces in the
...
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Implication of Fock matrix elements
In linear combination of atomic orbitals/molecular orbital based quantum chemistry theory, when the block of Fock matrix elements connecting occupied with virtual orbitals is zero, why does this imply ...
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1answer
76 views
What is the $Q_y$ transition in a bacteriochlorophyll?
Bacteriochlorophyll (BChl) are pigments that occur in the photosynthetic mechanisms of bacteria. I am studying some papers on the excitonic properties of BChl's, and the term $Q_y$ transition comes up ...
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156 views
Changes in Water Bonding Angle
I heard something recently in a casual discussion, but have yet to be able to confirm it: is there any evidence that the bonding angle for a water molecule, currently defined as 104.5, has been either ...
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1answer
68 views
How does the specific frequency of EM Radiation relate to displacing electrons from their orbits?
I've only a general grasp on how all this works, so it could be I'm asking this poorly or misunderstanding what happens. With that said:
The energy of EM radiation is a function of its frequency. ...
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1answer
285 views
Theoretical treatment of Hydrogen bond?
I would like to understand how the Hydrogen bond can be described through the Schroedinger equation. I don't need numerical methods that one uses them to simulate it, rather I need its treatment from ...
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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 ...
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1answer
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Number of unique 2-electron integrals
Consider 2-electron integrals over real basis functions of the form $$(\mu\nu|\lambda\sigma) = \int d\vec{r}_{1}d\vec{r}_{2} \phi_{\mu}(\vec{r}_{1}) \phi_{\nu}(\vec{r}_{1}) r_{12}^{-1} ...
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2answers
78 views
Driving a solution of optical isomer molecules with the resonant frequency
What happens when we drive a solution of optical isomer molecules (enantiomers) with a microwave radiation in resonance with the tunneling frequency of the molecules (the frequency of the transition ...
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1answer
152 views
Why do hydrogen atoms attract?
That is, why is the potential energy with the orbitals overlapping less than with the Hydrogen atoms 'independent'.
Similarly, why is a noble gas configuration stabler than if an electron were to be ...
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192 views
Minimizing the energy of a Slater determinant: why are the Lagrange multiplier elements of a Hermitian matrix?
If I want to minimize the energy of a Slater determinant subject to the constraint that the spin orbitals are orthonormal (as in the Hartree-Fock approximation), I can use Lagrange's method of ...
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1answer
164 views
Why are do neutral atoms shrink as their valence shells approach 8 electrons?
Why do neutral, unbonded atoms shrink in size as they approach having 8 electrons in their valence shells? A good example is elements 3 through 10 in this table, that is, lithium (1 valence electron) ...
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1answer
290 views
Density of classical states in quantum theory
Let's first treat electrons as classical objects. I can evaluate the classical energy of each state in a configurational space (3N real numbers and, say, spins) using just Coulomb's law.
Then I ...
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1answer
106 views
Experiment to find structure of water
Who first determined the structure of water (two hydrogen atoms stuck to an oxygen atom at approx 105 degrees), and, more importantly, how was this done?
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1answer
80 views
Does spin alone have any effect on the physical interactions of particles?
In Hartree-Fock theory the time-independent electronic energy of a single (restricted) determinant electronic wavefunction consists of one electron terms, $h_{ii}$, Coulomb interaction energies, ...
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381 views
Why is quantum physics needed to explain photosynthesis?
Why is quantum physics needed to explain photosynthesis?
In what aspect does the corresponding classical theories for photosynthesis fail?
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1answer
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Why is oxygen in a triplet state and what are the consequences?
From Wikipedia here and here:
''Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception.''
''The unusual electron configuration prevents ...
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2answers
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Why does iteratively solving the Hartree-Fock equations result in convergence?
[ Cross-posted to the Computational Science Stack Exchange: http://scicomp.stackexchange.com/questions/1297/why-does-iteratively-solving-the-hartree-fock-equations-result-in-convergence ]
In the ...
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1answer
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THT (Tetrahydrothiophene) absorption spectrum
I am looking for the absorption spectrum of THT. What is the best way to find these types of exotic material's spectral characteristics?
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2answers
777 views
Software to simulate and visualize atoms?
Not sure if this is a physics or chemistry question. But if the motion of atoms and it's particles can be described by quantum mechanics, then is there a software that simulate full atoms and it's ...
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47 views
catalysts as traces in a monoidal category
I was fooling around with string diagrams in a monoidal category and I was thinking about them in terms of chemical reactions. I wondered about bending a wire around and attaching it to the input of ...
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The Born-Oppenheimer approximation and muonic molecules
Does the Born-Oppenheimer approximation fail for muonic molecules (i.e. molecules where one or more electrons are replaced with muons)?
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1answer
166 views
Is it possible to mechanically isomerize an sp3 hybridized carbon center?
Imagine I have an sp3 hybridized carbon attached to four separate polyethylene chains. By pulling on the polyethylene chains in some manner, is it possible for me to mechanically isomerize the chiral ...
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1answer
202 views
Physical Chemistry: What's the relationship between orbital overlap and barrier shape?
This is a question for the physical chemists out there.
For a given chemical reaction there is a barrier to traverse in order to proceed from reactants to products. Reactants e.g. an organic base ...
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1answer
399 views
Is Palladium an exception?
I have been taught in school that atoms cannot have more than 8 electrons in the outer shell. Palladium atom's electron configuration is 2,8,18,18. Why isn't it 2,8,18,17,1 like the case of Platinum ...
