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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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 ...
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How to sloppy freeze a dihedral angle within a range in a Gaussian modredundant optimization?
I would like to perform an optimization in Gaussian 09 of my molecule with two dihedral angles being frozen. I would like that the values of these dihedral angles are not fixed, but can relax ...
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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....
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Is coupled cluster variational for two electrons?
I know that coupled cluster (CC) is not variational for the general case. However, if we only have two electrons with one nucleus, CCSD should be exact for this system like full configuration ...
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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 ...
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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.
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What is a degenerate orbital
I don't really get what degenerate orbitals are, I mean I know that orbitals are degenerate when they have the same energy level, and I know that the energy levels depend on n, but does that mean that ...
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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 ...
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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^...
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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. ...
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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 ...
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Physical interpretation of transition density matrix
I am studying natural transition orbitals (NTOs) and I am following the Martin's article [1]. I understand the mathematics, but I am a bit confused about what exactly is the transition density matrix ...
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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 ...
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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}...
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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
\...
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