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, ...).
1,571
questions
0
votes
0
answers
18
views
Why Car Parrinello Molecular Dynamics doesn't need an SCF calculation at every time-step?
Reading the various terms of the Lagrangian in CP-MD I'm trying to understand why there is not an SCF procedure hidden there.
In fact, it seems to me like the second term of the Eulero-Lagrange ...
- 101
-1
votes
1
answer
46
views
Why can we see color during d-d transition of electron? [duplicate]
As we know that when a ligand approaches the transition metals, the d-orbital loses its degeneracy and in this case electron can jump from lower orbitals to higher orbitals adsorbing the visible light....
-2
votes
1
answer
80
views
Why do we only use the principal quantum number to calculate the energy of an electron in an H atom? [duplicate]
According to my high school textbook the energy of an electron in a hydrogen atom is $E = -13.6/n^2~\pu{eV}$, where $n$ is the principal quantum number of the orbital in which the electron is present.
...
1
vote
0
answers
28
views
Gaussian Program Error for Linear Triatomic Molecule
I am trying to calculate the Hessian and vibrational frequencies of OCS (and eventually some anharmonic properties) with Gaussian09. However, the program always fails and I end up with the following ...
- 111
2
votes
1
answer
210
views
Why d orbitals oriented along $z^2$ axis assigned zero magnetic quantum number?
I have been studying quantum mechanics recently and I have come across this:
d orbitals oriented along the $z^2$ axis is assigned zero magnetic quantum number
I am wondering why specifically the $dz^...
- 211
0
votes
1
answer
47
views
Why we seldon use Fermi Surfaces to explain chemical behaviour? [closed]
Chemistry basically involves studying the behavior of electrons in atoms and their consequences. Solid-state physicists deeply study Fermi surfaces, analyzing the three-dimensional behavior of atoms. ...
- 224
2
votes
0
answers
33
views
Is the $2p$ RPD defined along the z-axis?
In MIT $5.111$ class (lecture $6$), we are to compare the most probable radius of a $2s$ orbital and a $2p$ orbital. The graph used by the professor represents the RPD versus $r$:
My question is: in ...
- 257
1
vote
0
answers
32
views
Doubly occupied orbitals in quantum chemistry? (openfermion.org)
I am interested in diagonalising the fermionic Hamiltonian of small molecules, such as LiH in second quantisation.
The Hamiltonian is
\begin{align}
H(R) = \sum_{ij} h_{ij}(R) a_i^\dagger a_j + \frac{1}...
- 111
1
vote
0
answers
67
views
Finding the relative position of the molecule in the adsorbate and adsorbent by minimizing the Hamiltonian
I am trying to model an adsorbing process (or more precisely, Heterogeneous catalysis process between solid catalyst and gas reactants). One of the step is to minimize the Hamiltonian by optimizing ...
- 77
0
votes
1
answer
68
views
Do Electron-Withdrawing-Groups give an hypsochromic shift or a bathochromic one? and why?
I'm not familiar with this topic,but i know that bathochromic shifts occur when the energy gap between energy levels of the substituted molecule, are lower than the unsubstituted one;viceversa ...
- 19
1
vote
0
answers
52
views
Absurd result for the selection rules in the three-dimensional PIB
By using time-dependent perturbation theory and some simplifying assumptions, we know that a transition for a charged particle $q$ from a quantum-mechanical state $m$ to $n$ is allowed if and only if
\...
- 3,669
1
vote
0
answers
68
views
In the RDF plot of a particular orbital, why don't peaks come with radius greater than that of the max peak?
While studying radial distribution function (RDF) plots I see that orbitals (3s, 2s, ... 3p etc) often have peaks at radii less than that of the maximum peak. Assuming the probability of finding an e-...
2
votes
0
answers
57
views
Why is the translational motion left out of the energy eigenvalue in the hydrogen atom?
When solving the hydrogen atom, since we have two particles, the wave function has the form $\psi(\mathbf{q}_1,\mathbf{q}_2)$. Generally, textbooks proceed to demonstrate that an interacting two-...
- 3,669
4
votes
0
answers
44
views
Helium ground state with Hartree–Fock using angular dependent functions
To compute the helium ground state (singlet) in Hartree–Fock theory we have to solve this equation:
$$ \left[ - \frac{\Delta}{2} - \frac{Z}{r} + \frac{1}{2} \int d^3 r' \frac{\vert \Psi(\boldsymbol{r'}...
- 41
-1
votes
1
answer
108
views
How does an electron's distance from the nucleus depend on angular quantum number?
My school teacher told us this and I couldn't get his reason:
The average distance of an electron (belonging to the same orbit) from the nucleus decreases with the increase in the value of angular ...
- 127