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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How to compute solvent reorganization energy in Marcus' non-equilibrium approach?
I try to solve the following equations for some system solvated in the water. The goal is to obtain value in kcal/mol. Unfortunately, I cannot reach the desired output. May someone help me?
The ...
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How to display atomic charges from MOPAC calculation?
MOPAC (http://openmopac.net/) is nice semiempirical code. It also calculates charges on atoms.
Is there a free GUI to display them please ? What I know, Avogadro diplays vibrations, JMol orbitals......
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Molecular orbital energies for CH4 using group theory
I was learning how to use symmetry in molecular orbitals, I started with $\ce{CH4}$ the point group is $T_d$ I get the reducible representation for methane the reduce it to be $T_2+A_1$, the I applied ...
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Determination of ground state energy that has the same L and S values
Determination of the energy of a multielectron atom in the ground state can be estimated using the atomic term symbol which involves the values L, S and J. If an atom has the same L and S values ...
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Can geometry of a molecule change when the spin-orbit coupling is taken into account?
Cross-posted on MMSE.
Is there any evidence that spin-orbit coupling (SOC) leads to significant changes in atomic structure? Using DFT, I am getting different relaxed lattice constants when I take SOC ...
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How to perform NBO calculations at each point while scanning the bond length?
For a given bond, I would like to perform an NBO calculation for each structure while scanning the bond lengths.
Can I use Opt=ModRedundant in combination with pop=nbo? Simply specifying both ...
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How to calculate the ground state molecular potential curve of Lithium in different spin configuration?
I am a physics student and interested in Atom, and molecule optical physics. I am studying Feshbach resonance and I need to know the potential curve of the molecule, then I ask question in physics ...
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Critical point from ab initio calculations
I was wondering if it is possible to calculate the critical point (e.g., temperature, pressure, and density) other than via experiments or equations of state like ab initio calculations.
Would anyone ...
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Mulliken Labels: How do I tell apart E, doubly degenerate, symmetry apart from T, triply degenerate, symmetry for a molecular orbital?
With A and B, it's pretty simple. If you rotate the molecule about its principle axis to where the orbitals line up, and the signs change, it's Mulliken label has a B. otherwise, it's A.
I heard E ...
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Why is the statement regarding the strength of ionic bonds reasonable? [closed]
In largely ionic compounds (e.g. NaBr and NaI), it seems to be generally true that, the greater the differences of electronegativity between the forming substances (i.e. The compound has more "...
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Band structure of solids in general
As my last question (Semiconductors and their electronic bands) was badly structured, I decided to elaborate my questions a bit.
As I now know, every solid/liquid forms a band structure, so all ...
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What can be inferred from overlap matrix S if coefficient matrix C is unitary in Roothaan equation?
I was going through the Hartree-Fock algorithm, transforming the spatial molecular orbitals {$\psi _i$} to be a linear combination of Roothaan basis set {$\phi_i$}. From my knowledge {$\psi_i$} is set ...
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Effective Core Potentials and their "corresponding Pople" basis set
Reading through a handout from Yale shows the author correlating the ECP with Pople basis sets. The author of this says the corresponding basis set for SDD is 6-31G, Def2TZV as 6-311G, LANL2MB as STO-...
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Why is cyclohexane more polarizable than benzene?
Looking at figure 4.2 here, we can see experimentaly that cyclohexane is more polarizable than benzene.
Why is this the case?
Intuitively, I would think that because the orbitals in benzene are more ...
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Term symbols in transition metals and lanthanides
Hello I was researching a little about term symbols of lanthanides and transition metals and have got two questions.
It is known that lanthanides don’t follow LS-coupling, but instead JJ-coupling. ...
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How can I calculate the electrostatic energy between two fragments?
I have a 2-fragment molecular complex with partial charge transfer from fragment 1 to fragment 2. The binding energy is ~0.3 eV and I want to evaluate what fraction comes from electrostatic attraction....
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Eigenfunctions of total angular momenta as linear combinations of Slater-determinants
In the Hartree scheme for many-electron atoms, the approximated Hamiltonian (in a.u.)
$$\hat{H} = \sum_{i=1}^Z \left(-\frac{1}{2} \nabla_i^2 -\frac{Z}{r_i} + V_\text{H}\left(r_i\right)\right)$$
is ...
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Quantum chemistry and covalent bonding
How can the formation of a covalent bond be described from a quantum perspective, and what implications does it have for traditional chemical bonding theory?
Specifically, in the context of many-...
user137105
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Reduction of direct product representation
When we do the reduction of the reducible representation generated from the total wavefunction expressed as product of MOs of appropriate symmetry, we can find the direct sum of more than one ...
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Group theory and exact Eigenfunctions of Hamiltonian
I think I've understand why the real Eigenfunctions of Hamiltonian belong to a given irreducible representation and I've read that also MOs have to transform as irreducible representation due to the ...
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What does the 2 in t2g stand for?
I have read so far that it is about whether the d-Orbital is symmetric to a C2 element perpendicular to its main rotational axis. If all the given orbitals in a group are symmetric to that element, ...
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Commutating operators of angular momenta
I've studied the formal procedure to pass from the uncoupled basis set of individual angular momenta to the coupled basis set of total angular momenta for polyelectronic atoms.
I start from an ...
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Why don't I get a whole number when determining the vibrational energy level of F2? [closed]
This is a cross post from physics stackexchange. I hope to get more answers here, because I think chemists have more to do with such things.
So I was playing around with some data and formulas and ...
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Electron energy shells/ levels
Essentially, I am told electron shell closest to the nucleus is the lowest energy level and subsequent shells have higher energy (I.e. those further from the nucleus).
But..... electrons in the ...
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"Probability flux": Imaginary part
I was confronted with this problem from "Mathematik für Chemiker", 8th edition (Ansgar Jüngel, Hans G. Zachmann):
$$ \begin{align}
\partial_t |\psi|^2
&= \partial_t (\bar\psi\psi) \\
&...
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Some advice on inorganic textbook [duplicate]
I'd like to have some advice on Inorganic textbooks.
I've already consulted some books (Kettle, Drago, Keiter, Cotton) and they are all very useful, but now I'm searching for a textbook which focuses ...
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Doubt on vibronic transitions
When we justify the presence of electronic transitions forbidden by Laporte selection rule, the coupling between electronic and vibrational states help us. Why we say that in this way we are ...
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Principal quantum number and 'good' quantum numbers
When we discuss about configurations we specify n, l, m quantum numbers for the individual electrons.
My question is: why when we pass from configurations to atomic terms in order to use the total ...
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Hartree-Fock calculations of the states of Nitrogen molecule ion
I was reading the third chapter of "Modern Quantum Chemistry" by A. Szabo and N. Ostlund about HF calculations, and in the end of the chapter it shows as an example a calculation on $\ce{N2}$...
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Why is there a point of orbits along with quantization in case of energy gaps?
As per my textbook and online sources. The definition of Energy bands I have found is this:
A) Energy levels:
( In a simplified view of an electronic structure of a single atom or isolated molecule.
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Refrence on shielding effect vs inter electronic repulsion
Recently I came across a very interesting concept , some scholars were saying that -
Shielding accounts just one component (radial) of interelectronic repulsion not complete repulsion
Who they are -
...
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Fluorescence and resulting vibrational state
I was taking a look at Jablonski schemes and had some doubts regarding it. Now assume a regular molecule which follows this Jablonski scheme:
We can see that when molecules absorb certain quantized ...
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electron - electron repulsion and shielding effect [closed]
What is difference between shielding and electron electron repulsion. When I read this article , I came to know that both are different. First Read this paragraph and see the graph of ionization ...
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Ionization and exchange energy [closed]
As we all know that 'Nitrogen' has higher 'Ionization Energy' than its neighboring elements both carbon and oxygen, opposite to the trend of increasing ionization energy across a period. The reason ...
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Are the inner circular rings in higher 's' sub shells part of inner 's' sub shells, as the diagrams suggests?
The diagram of, for example, 2s and 3s, is the innermost circle showing electron probability has to be 1s subshell. How could it be the part of 2s or 3s, since it is a complete circle around nucleus ...
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How do the orbitals in atoms synchronize their phases during the formation of a bond?
Suppose I have two hydrogen atoms, each with one electron in their 1s orbital. Then we can represent the wave functions of these two as say $|\Psi\rangle_1$ and $|\Psi\rangle_2$ for each of the two ...
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Software to draw one-dimensional PES including vibrational energy levels
I am trying to represent the difference between the an anharmonic and harmonic treatment of vibrations. The easiest way to do this is to present an example of a harmonic and anharmonic potential ...
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Can excited electronic states also decay due to collisions?
I was wondering if electronic states could decay due to collisions and not by fluorescence?
Just like vibronic relaxations can happen, when vibrationally excited molecules can lose those extra modes ...
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Deriving the equation of motion for adiabatic approximation
In the textbook, Theories of Molecular Reaction Dyanmics by Flemming Y. Hansen and Niels E. Henriksen, there is a derivation of the equation of motion for the adiabatic approximation (pgs. 5-7). The ...
user129490
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How Can the First Ionization Energy of Helium be Accurately Calculated Using Basic Quantum Mechanics?
How Can the First Ionization Energy of Helium be Accurately Calculated Using Basic Quantum Mechanics?
There is a book which summarizes the fairly accurate calculation of the First Ionization Energy of ...
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Combining two overlapping wavefunctions
Let's assume that we solved the many-body Schrödinger equation for two molecules and we can now write their wave functions as
$$
|\Psi_1\rangle = O_1|\operatorname{vac}\rangle\,,\\
|\Psi_2\rangle = ...
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Atomic terms and perturbation theory
I have a question about the derivation of the possible atomic terms of an atom. Consider an atom with $N$ electrons in the central-field approximation, with hamiltonian
$$
H_{0} = \sum_{i=1}^{N} \left[...
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Why are p orbitals most important for stability? [closed]
Is there nice way to see/show/derive why p orbitals are so important for stability? Or asked differently: Why are elements with filled p orbitals on the right side of the periodic table? Why aren't ...
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Franck-Condon principle and shift of wavelength
I was revisiting my notes for spectroscopy, and I came across the Franck-Condon-principle. I understand it well, but want to clear some doubts regarding this.
I know that the Franck-Condon-principle ...
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Why SCF-MO methods fail when treating bond-breaking processes?
I'm currently studying the EVB(Empirical Valence Bond) approach. While reading on this article (https://pubs.acs.org/doi/10.1021/ja00224a011), the author mentioned about the usage of SCF-MO formalism ...
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Jablonski diagram and absorption
I was reading about Jablonski diagrams and how they are structured. Bold lines would indicate ground electronic levels, and thin lines indicate the associated vibrational levels. Absorption only ...
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Derivation of the conversion of Gaussian type orbitals (in cartesian coordinates) to Gaussian type orbitals (in polar coordinates)
While studying basis sets, I came across Gaussian type orbitals (GTOs), which are used as atomic basis sets. I reviewed the polar form of these orbitals, which are very similar to hydrogen atom ...
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Distance of Orbitals from Nucleus relation with Energy level and penetration power
I have studied that according to Aufbau rule the energy of subshells is dependent on the sum of $ n $ and $l$ values. This would imply that the energy of subshells in a shell varies as
$$ ns \lt np \...
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Obtaining transition density matrix
I'm trying to assemble a transition density matrix on quantum computer using one-body excitation $\widehat{E}$ operator on 2 active spatial orbitals, i.e. on 4 spin-orbitals. The problem is, I need to ...
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Auxochrome groups and red shift
Wikipedia states that "An auxochrome is known as a compound that produces a batochromic shift, also known as a red shift because it increases the absorption wavelength, thus approaching infrared ...
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