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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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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'}...
fefetltl's user avatar
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1 answer
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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 ...
Rishikesh's user avatar
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Integrating out spin in 2-electron energy function

I am just starting to learn Quantum Chemistry for my research. I am currently reading Modern Quantum Chemistry by Szabo and I am a little confused by a concept. The two-electron ground state energy is:...
Michela's user avatar
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2 answers
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Why aren't there different peaks for different IE in PhotoElectron Spectroscopy (PES)?

The way I understand PES is that you shine a light on a bunch of atoms and measure the kinetic energy of photons to determine ionisation energies (or energies of electrons... is that different?). I ...
Maddy's user avatar
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1 answer
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Frequency to induce nitrogen inversion

I would like to know how to compute the frequency at which nitrogen inversion happens in ammonia gas at STP. The activation energy for such process is 24.2 kJ/mol, therefore I thought that it is ...
crisecon's user avatar
1 vote
0 answers
5 views

How to perform LC-BLYP calculation with GAMESS? [migrated]

I am currently working on time-dependent density functional theory (TDDFT) calculations for both singlet and triplet states using the LC-BLYP functional in GAMESS. I believe I have correctly followed ...
Alireza Lashkaripour's user avatar
-2 votes
0 answers
34 views

Why is the concept of penetration power only applied to Be and B, and not to Be and C, N, O, F?

In my book, it is stated that the ionization energy of Be is greater than that of B because the electron removed in Be is in the 2s orbital, while the electron removed in B is in the 2p orbital. This ...
Peter swift's user avatar
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1 answer
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Degeneracy of Orbitals

(Sorry, in advance if my question is silly or low quality but I want to ask this to someone.) When an electron enters an orbital, it should technically have an electric Field and also magnetic field(...
Krave37's user avatar
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3 answers
117 views

Challenging Orbital Restrictions

According to the n-l-1 formula for nodal count, wouldn't 1p, 1d, and 1f orbitals be possible since l (angular momentum quantum number) can be 1, 2, and 3 respectively for a principal quantum number (n)...
White knight's user avatar
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Why aren't other elements with valence 6s electrons liquid like mercury?

I found out that mercury's 6s electrons undergo relativistic effects that make their pull to the nucleus greater, which makes it so that they can't bond with other atoms of mercury to form a solid. ...
ilikemath12783's user avatar
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1 answer
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Stability of atomic/ionic quantum states in relation to the full octet rule

We have started our Chemistry Unit and the very first statement the teacher says is that "All Atoms want to be stable. They achieve this by having a full valence shell, which they achieve by ...
Dev P.'s user avatar
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1 answer
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Wave function in Schrodinger's model

I am trying to wrap my head around the Schrodinger's quantum mechanical model of an atom. According to the NCERT$^1$, the Schrodinger's equation is given by: $$\hat{H}\Psi=E\Psi$$ where $\hat{H}$ is ...
Harikrishnan M's user avatar
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0 answers
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Resonance stabilization : lowering of kinetic energy or electron repulsion?

Resonance stabilization, or delocalization stabilization, occurs when the overall energy of the molecule is lowered compared the localized "resonance structures". In solid state physics, or ...
Félix Faisant's user avatar
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0 answers
61 views

The sign of the lobes in an atomic orbital

In atomic orbital diagram of an atomic orbital, the lobes are represented as either positive or negative. It is said that the wave function is 'positive' where the lobe is depicted positive and '...
Nothing's user avatar
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How to find the global minima of a supramolecular complex in computational chemistry?

So this is more of a complex problem, and my masters thesis could greatly benefit if I find an answer to this. Essentially, I have a supramolecular inclusion complex. There is this molecule A (the ...
VASUDEVAN K 's user avatar
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1 answer
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Does ionisation change the physical/chemical properties of an atom?

From what I have learned, the number of electrons on the outermost shell (called the valence electrons), determines the chemical properties of an atom, this is why elements in the same group have ...
user144179's user avatar
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What are some general chemistry textbook with good problems? [duplicate]

I’m currently in a General Chemistry course and am wondering if you guys can recommend me a textbook or resource where I can find good problems to work through and further my understanding. We’re ...
Joel's user avatar
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How does more s character shorten bonds and strengthen bonds?

I'm aware that having more s character means that electrons are in the lowest energy state (?) and very close to the positive atomic nucleus. But then what’s the connection between having electrons ...
Ki Ki's user avatar
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5 votes
0 answers
153 views

N2 HOMO-LUMO Gap calculation

I am thinking about calculating the HOMO-LUMO energy gap for $\ce{N2}$ molecule. I thought I could model this as a particle in a box problem to find $E_\text{HOMO}$ and $E_\text{LUMO}$. The formula I ...
kevin Tah N.'s user avatar
2 votes
1 answer
91 views

Grade 12 chemistry question about Schrodinger's standing wave?

this is my first time ever using a website like this but I have something I'm curious about. My chemistry teacher showed this today (img below) and discussed how quantum of energy that hits the ...
randomgrade12student's user avatar
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Difference between HOMO and LUMO and corresponding spectral gap in Hamiltonian

Coming from a Quantum Computing background, I am familiar with the singular value definition of spectral gap, I am currently trying to run Quantum Chemistry simulations and I would like to know if $|\...
Zee's user avatar
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4 answers
224 views

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 ...
lynx_s's user avatar
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1 answer
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Quantum Mechanics expectation value help

I am working on the following question: I've so far done the first part of a, finding $H_{so}$ in terms of J L and S. I'm struggling to see how to relate that to $E_{LSJ}$ as it involves the ...
chem12314's user avatar
2 votes
1 answer
147 views

Mechanism of adhesion of particles on solid surfaces [closed]

What is the mechanism of adhesion of particles on solid surfaces? How does anything stick to anything, for that matter? Why does cigarette smoke stay so stubbornly on our bodies? Why does perfume also ...
damacc's user avatar
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Theoretic (QED) Atomic Ionization Energies Database?

The 2019 paper "QED tests with highly-charged ions" contains a survey of QED-calculated atomic ionization energies. I can manually copy the values of interest therein, but it seem that ...
James Bowery's user avatar
1 vote
1 answer
299 views

Why does graphite have a higher standard molar entropy than diamond?

It is known that graphite (5.7 J/K mol) has a higher standard molar entropy than diamond (2.4 J/K mol) (data from Physical Chemistry by Atkins). I understand that this must be due to the structural ...
astroleaf's user avatar
0 votes
1 answer
83 views

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 ...
farmaceut's user avatar
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2 votes
1 answer
89 views

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......
Miro Iliaš's user avatar
1 vote
0 answers
26 views

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 ​​...
Jots's user avatar
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5 votes
1 answer
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Can geometry of a molecule change when the spin-orbit coupling is taken into account? [closed]

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 ...
freude's user avatar
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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 ...
user139725's user avatar
1 vote
0 answers
33 views

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 ...
Hsu Bill's user avatar
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0 answers
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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 ...
Emerson P L's user avatar
8 votes
2 answers
555 views

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 ...
AdamT's user avatar
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-2 votes
1 answer
72 views

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 "...
蕭力諶's user avatar
1 vote
1 answer
223 views

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 ...
Mäßige's user avatar
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0 answers
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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 ...
chikako's user avatar
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0 answers
51 views

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-...
MrAmateurChem's user avatar
2 votes
0 answers
182 views

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 ...
McKinley's user avatar
1 vote
0 answers
155 views

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. ...
Mäßige's user avatar
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0 answers
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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....
Nick Kateris's user avatar
4 votes
1 answer
271 views

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 ...
Simone's user avatar
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2 votes
1 answer
176 views

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-...
user avatar
0 votes
0 answers
45 views

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 ...
Chemistry.'s user avatar
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0 answers
51 views

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 ...
Chemistry.'s user avatar
2 votes
2 answers
435 views

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, ...
Rivinius's user avatar
2 votes
0 answers
41 views

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 ...
Chemistry.'s user avatar
1 vote
2 answers
100 views

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 ...
iwab's user avatar
  • 359
-1 votes
1 answer
50 views

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 ...
Elaine Gerrard's user avatar
6 votes
1 answer
135 views

"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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