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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107 views

How fast do electron's quantum spin flip?

In a recent lecture it was taught that carbenes with their electrons in a triplet configuration do not undergo concerted reactions as one of the electrons must first undergo a spin flip; on what ...
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56 views

Computational chemistry: is k a quantum number

I am trying to use the natural band offset method to calculate band offsets of junctions. In order to do so, I need to find the core electron eigenstates. I tried using FP-LAPW software Elk. But in ...
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469 views

How does symmetry of half filled and fully filled orbitals lead to stability

I googled a lot about why symmetry of half filled and fully filled orbitals decreases their energy but every time it is repeated that symmetry leads to stability. So the question is why symmetry leads ...
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217 views

Particle in a box models for polyenes and quantum dots [duplicate]

I'm kind of new to physical chemistry and trying to understand how, if at all, the correspondence principle (in the limit of large quantum numbers, quantum mechanics reproduces classical behavior of a ...
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311 views

Radial nodes in molecular orbitals

Do radial nodes exist in molecular orbitals? Radial nodes exist in atomic orbitals and the number of radial nodes for an atomic orbital can be determined by the general formula $n-l-1$ where $n$ is ...
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44 views

determine at which v and J the rotational and vibrational energy differences are equal

I was presented with this question and I started working on it but I ran into a problem. We've got $\Delta E_{rot} = 2B_e(J+1) $ and $\Delta E_{vib} = \hbar \omega$ We get to the point that we've ...
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537 views

Gaussian: Warning - assumption of classical behavior for rotation may cause significant error

I am playing around with a prostaglandin molecule (23 heavy atoms) in Gaussian09. My goal is to calculate the vertical ionization potential and electron affinity for the molecule. I already managed to ...
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35 views

Which MO approximation best fits with lab results and observation? [duplicate]

I understand that there are many different methods that can be used to approximate the set of MOs for an arbitrary molecule, as the actual quantum mechanical description is taxing to calculate. I just ...
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48 views

phase differences between conical intersections and light-induced conical intersections?

I've read recently about light-induced conical intersections, a phenomenon where conical intersections can be artificially introduced to molecules, and that this can be observed even in diatomic ...
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115 views

Calculating Optical Absorption Spectra using Ab Initio Computations

My main question is, How does one compute the optical absorption spectra of a molecule by using say, Configuration Interaction energy and associated transition dipole moments. I am trying to use an ...
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126 views

How do i make an molecular orbital diagram step by step?

My professor explained me, but i'm still unable to do a correct molecular orbital, for a diatomic molecule
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51 views

Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational ...
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759 views

Physicist notation for spatial orbital

In quantum chemistry, the two-electron integrals often denoted as physicist's and chemist's notations. For spin orbital, the physicist's and chemist's notations are $$ \langle pq | rs \rangle = \int ...
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163 views

Conical intersection using GAMESS

I would like to know how to locate conical intersection using a GAMESS calculation. I really appreciate an example alone with this since I am a novice I do not have a clear idea among bunch of ...
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39 views

Identifying the dependence of various time-independent wavefunctions

I'm tasked with finding the variables that each of the following wavefunctions depends on: (1) a free particle in 2 space (2) a free particle in 3 space (3) a hydrogen atom (4) a lithium atom. for ...
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62 views

Excitation Source for visible emitting Quantum dots

I read that the best excitation source for visible emitting quantum dots is UV light of wavelength $\mathrm{360~nm}$ to $\mathrm{380~nm}$. But why should the excitation source have lower frequency ...
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179 views

Use of statistics in this field

I am currently pursuing a statistics course and I an interested in knowing how can statistics help this field in future. (I am interested because I love chemistry very much) Specifically, are there ...
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46 views

Sulfur atomic absorption

Would the atomic absorption from FAA for Sulfur be from 3s2 -> 3p4 or 3p4 -> 4s0? I think according to the electronic partition function, there would be zero electrons in the 4s0 state at the ...
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82 views

Help solve this specific linear schrodinger equation, please

$$\left[-\frac{1}{2}\nabla^2 - \frac{2}{r} + C\right]\phi(r) = E\phi(r)$$ where $C$ is a known function. I am just looking for some help on the strategy to solve explicitly for $\phi(r)$. One thing ...
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321 views

How do I calculate principal quantum numbers of the Lyman series

How do I calculate principal quantum numbers of the Lyman series? I've been given that the lowest line is 121.6nm and the 5th line is 93.8nm The formula of the wavenumber is v=-R(1/n2^2 - 1/n1^2) ...
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358 views

QMOT | Orbital mixing in methyl

The following picture is from E. V. Anslyn Physical Organic Chemistry and shows constructing of MO of methyl using QMOT. MOs $\textbf{E'}$ and $\textbf{D'}$ are formed by mixing $\textbf{D}$ and $\...
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Experimental Validation of Schrodinger's Electron Cloud theory

I am currently doing a report for school on the electron cloud atomic structure theory. One of the major points on my report is the experiments performed by the scientists (Schrodinger and Heisenberg) ...
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196 views

Number of orbitals in full configuration interaction

I am using one quantum chemistry package where I am supposed to assign a number of active orbitals I want to be included in the FCI (full configuration interaction) calculation. For example if I have ...
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1answer
1k views

What are the magnetic quantum numbers for specific d orbitals? [closed]

I mean I know they’re $\ce{d_{-2}}$, $\ce{d_{-1}}$, $\ce{d_{0}}$, $\ce{d_{1}}$, $\ce{d_{2}}$ but how do these numbers relate to each one of $\ce{d}$ orbitals $\ce{d_{z_2}}$, $\ce{d_{xz}}$, $\ce{d_{yz}}...
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Physical Meaning of the Difference between MO and VB Wave Function of H2?

What would be the physical meaning of the difference between the MO wave function and VB wave function of $\ce{H2}$?
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What happens when we heat an atom?

Question is simple.. If we take an atom of any element and then supply heat energy to it then what will happen? What I thought is that in the beginning, energy (quanta; due to excitement of electron ...
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2answers
58k views

How to find the number of valence electrons?

I need to understand the following: Considering an element Sulfur - S which has 16 electrons. How do we calculate the number of valence electrons of S? Please correct me if I am wrong:2+2+6+2+4=16. ...
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1answer
824 views

How to calculate probability of finding an electron at a point?

In school i learned how to calculate probability of finding electrons in some volume but how can we calculate the probability of finding a electron at a particular point. Point here ...
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1answer
667 views

H2 Triplet State

How does $\ce{H2}$ triplet state exist if there are electrons in both bonding and antibonding ($1\sigma$ and $1\sigma^*$) orbitals? Or am I being taught the hypothetical triplet states of the ...
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1answer
126 views

Electron vs electron density

I recently read somewhere that electrons do not exist. it's just the electron density. Is it true that there are no electrons (particles) but only in the form of electron density? And does this ...
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2answers
81 views

Spin Operator algebra

I am trying to teach myself some QM. In Christopher J. Cramers textbook Essentials of Computational Chemistry: theory and models, in Appendix C, he goes over Spin algebra. I am unable to calculate ...
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2answers
82 views

Hamiltonian 2nd positional derivative analogous to acceleration?

In Quantum Mechanics, we learn that the Hamiltonian operator for an electron confined to a 1-D space is: We learn in QM that many operators have analogous interpretations familiar to us from ...
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1answer
816 views

Degenerate orbitals in the Hydrogen atom

I came across the following link: Which orbitals of the hydrogen atom are degenerate for $n=3$ And all the answers said that for the hydrogen atom, the energy of an orbital depends only on n. Is ...
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1answer
93 views

when do we indicate the “+ or -” sign in uncertainty [closed]

how can we know when to indicate "+ or -" sign in uncertainty calculations because I noticed some problems has been solved by this sign and some has not.
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1answer
111 views

Quantitative MO theory- how is the overlap integral and the weighting coefficients of the molecular orbital actually evaluated?

Title. In my inorganic chemistry course, we learn about SALCs and qualitative MO treatment, with only a fleeting reference to the S integral and actual molecular wave functions (only hydrogen, $\ce{H2}...
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1answer
172 views

Relationship between the first and the second quantum number

Does the secondary quantum number tell how many subshells a specific principal quantum number shell has? E.g., if the principal quantum number is $n$, there are ($n-1$) subshells.
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1answer
64 views

antisymmetric wavefunction [closed]

Why can't we choose any other antisymmetric function instead of a Slater determinant for a multi-electron system? Why do we choose our wavefunction for a multi-electron atom as a product of single-...
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1answer
83 views

Why is the volume related to the probability of finding an electron? [closed]

thank you for your time. I was wondering about the correlation between volume and probability of finding an electron. we know that if we move away from the nucleus, we are going to get less ...
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1answer
854 views

Angular Momentum Of S-subshell of an atom?

The angular momentum of every S-subshell of an atom is 0 by Azimuthal Quantum No. Relation. But if angular momentum of S-subshell is zero. Then by, Angular Momentum =Mass×Velocity×Radius; Radius of S-...
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1answer
2k views

Which is the bigger ion, F- or O-?

Well, according to the proton-electron ratio $\ce{O-}$ should be bigger than $\ce{F-}$ What about the charge/electron density in $\ce{F}$? Will it not affect the size of the atom of $\ce{F-}$?
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1answer
48 views

Quantum mechanics electron probability [closed]

Schrödinger's equation yields us the solutions of 90% probability of presence of electrons in orbitals. Hence, the electrons in theory should be able to exist elsewhere in space as well. In that case, ...
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1answer
53 views

Expression of the potential in the hydrogen atom while solving radial part of the wave function

I was reading about the derivation of wavefunction of Hydrogen atom from Atkins book. After the separation of variables and writing the wave function, $\psi_{(r,\theta,\phi)}=R_{(r)}Y_{(\theta,\phi)}$...
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1answer
53 views

Do quantum particles have mass? [closed]

Quantum particles are never objects but are always waves. But do they have mass or can they carry mass?
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62 views

Why is atomic orbital one electron wave function? Why distance from centre is proportional to angular wave function?

Consider the following statements: An atomic orbital is one electron wave function $\psi(r,\theta,\varphi)$ obtained from the solution to the Schrödinger equation. There two electrons in an atomic ...
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2answers
73 views

Confusion in half filled or full filled electronic configuration

At the end of electronic configuration, we were taught that, electron orbitals are most stable when they are either fully filled or half filled. E.g., the final valence configuration of chromium is $\...
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1answer
47 views

On the meaning of distinguishability, and wavefunctions for 3 electron atoms

In a 2-electron atom at lowest energy, the $(1s)^2$ is occupied and the electronic wave-function must satisfy anti-symmetry requirements in the particle coordinates, as the spatial wave function is ...
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1answer
125 views

Why does the d orbital size decreases on addition of electrons?

In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), on page 80 under section 3.7 "The Extent of d-orbital Participation in Molecular Bonding" it is given: A second ...
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1answer
87 views

Quantization and Bohr's model

According to quantization it's said that emitted or absorbed energy is quantized. Then, when it's said in bohr's model an electron changes its orbit (Let's say it goes to a higher energy shell from $...
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1answer
2k views

Where is the probability of finding an electron in 1s orbital maximum? [duplicate]

So the way I understand the question is that it asks us at what r (distance from nucleus) and at what angles is the probability going to be maximum. The way I see probability of finding at a point in ...
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2answers
130 views

What is the wavelength of an electron?

The kinetic energy of an electron is $1.67 \times 10^{-17}\mathrm{J}$. Calculate the wavelength ($\lambda$) of the electron. I know the formula $\lambda= \frac{h}{mv}$; where h is Planck's constant. ...