Questions tagged [molecules]
The molecules tag has no usage guidance.
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What exactly falls into the category of intermolecular forces and van der waals forces
So I read the wikipedia and its catagorization is somewhat vague. (Link here: https://en.wikipedia.org/wiki/Intermolecular_force)
In wikipedia, the van der waals forces are quite clearly stated to ...
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Do the molecules inside a dielectric physically move when the dielectric is polarized by an external electric field?
Today a colleague and I had a heated debate over whether, when an external electric field is applied across a dielectric, the molecules in the dielectric actually move/rotate (flip to align with the ...
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Electric dipole vs density gradient
Chemist here, so please excuse me for asking trivial stuff.
I am trying to represent the electron density of a molecule as a bunch of point charges.
One program that I use can calculate electron ...
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Generalized Lotka–Volterra equations to explore filling of energy levels in mixtures of interacting diatomic molecules
Did anyone saw any application of Generalized Lotka–Volterra equations to explore filling of energy levels in mixture of interacting diatomic molecules. The idea is to consider molecular interaction ...
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Double nomenclature of molecular orbitals
I'm studying molecules from Brandsen-Joachain's book: "Physics of atoms and molecules". In chapter 9 he talks about molecular orbitals, and then he specifically talks about them for ...
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Is many-electron system's energy bounded from above?
A many-electron system with molecular Hamiltonian under the Born-Oppenheimer approximation has a finite ground state energy, which means its eigenenergy is bounded from below.
In my research, I need ...
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Symmetry of the hydrogen molecule wave function
Due to their overlapping wave functions, electrons in an $H_2$ molecule must posses opposite spins. The nuclei (two protons) on the other hand are far enough apart for the Pauli exclusion principle to ...
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Derivation of particle distribution in a gravitational field
I'm trying to figure out where my logic is failing in the derivation of the concentation of particles with respect to the height in constant temperature and gravity ($n(h)$).
So we have the following ...
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On completeness of a set of commuting operators for homonuclear diatomic molecules
The electronic Hamiltonian for a homonuclear diatomic molecule is $$\hat{H}=-\sum_{i=1}^N \frac{\hbar^2}{2m} \nabla^2_i -\sum_{i=1}^N \frac{Z_Ae^2}{4\pi\epsilon_0|\vec{r}_i-\vec{R}_A|} -\sum_{i=1}^N \...
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Why does "Vacuum UV" start at 200nm?
According to here Vacuum UV is UV light with a wavelength of less then 200nm.
I've been told here that the reason why thoses ranges of UV are strongly absorbed by the air is that those photons have ...
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What is the state of the art in nanophotonic biosensing?
Over a decade ago I've been doing research in nanophotonic biosensing and all the reviews from those times were very impressive. Some plasmonic structures were capable of single-molecule detection and ...
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What does the radius of Fermi-Surface or the wavevector says about the occupied electronic states?
I have the following task:
Consider a simple cubic structure with a lattice constant of 0.3 nm and one atom per unit cell; the
macroscopic crystal has a size of 1 cm³. Assume that each atom ...
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Mean free path of molecules
So in the book concepts in thermal physics(by Stephan and Katherine Blundell) the expression of mean scattering time is derived as shown(please refer the book for more). If we replace vdt in the ...
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Are subshells and orbitals quantised the way shells are? [closed]
It is known that electrons can occupy only certain fixed energy levels in an atom and can gain or release photons of certain frequencies to move between shells.
Does it also hold true for subshells ...
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Question in High pressure high boiling point
I'm Finding it hard to visualize how higher pressure makes the boiling point higher. I understand how pressure increases then temperature increases such that say air molecules compressed gives it ...
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Why is the heat capacity of water $9R$ and not $6R$?
From the equipartition theorem, the relationship between energy and temperature in a substance is $U=\frac{NRT}{2}$ for $N$ quadratic degrees of freedom associated with a particle of that substance. ...
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Trying to derive the potential energy of an ionic crystal!
If we consider an ionic crystal of ions $A^+$ and $B^-$. We consider N ion pairs. Now I am trying to derive the formula once by considering the number of pairs and once considering the number of ions.
...
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Where does this (hydrogen molecule energy) graph come from?
I was thinking about the good old question of 'Why do molecules have lower energy than the atoms?'
And in a video (around 6:15), this good old energy graph is shown, which is stated as the 'answer' to ...
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Atoms or molecules as strongly correlated systems
Electrons in atoms or molecules are of course correlated, in the sense that the many-electron wave function is not a Slater determinant. However, in my personal impression, the Hartree-Fock ...
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Antimatter structures and chirality
I'm curious whether the reversal of spin number in antiparticles vis-a-vis their matter counterparts would have a corresponding reversal of the chirality of structures made of antimatter (over scales ...
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Shouldn't there be 3 antibonding orbitals for diatomic hydrogen?
The bonding state of H2 is |Ψ+>|0,0>. This makes sense because there is only 1 spatially symmetric state, in which the electrons experience an attractive exchange force. (|Ψ+> denotes spatial ...
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Why is the antisymmetric wavefunction for a $\rm H_2$ ion higher in energy and why can no stable molecule be formed in this state?
I just want to make sure my basic understanding of this is correct.
When the internuclear distance is finite, the symmetric wavefunction of the electron is lower in energy because it experiences a ...
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Do Van de Waals forces occur between macroscopic non-conducting objects?
Van de Waals (VdW) forces are intermolecular forces that are for example, due to spontaneous polarisation effects between atoms. As far as I understand, they occur between any type of atom/molecule/...
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Excitation energies of molecules
How are the excitation energies of molecules "formed"? Are they simply the sum of the excitation energies of their single atoms or do they also or instead provide further ones?
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How do I interpret the single electron Hamiltonian contribution in the Roothan-Hall equation?
I am currently going through Molecular Modelling: Principles and Applications by Andrew R. Leach (2nd Edition).
The Hamiltonian operator for an electron is given in equation (2.125) as
$$\mathscr{H}^{...
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What does a $\tilde{a}^3 A^{\prime \prime}$ molecular state mean?
In a paper (doi:10.1016/j.theochem.2005.03.035) they discuss the $\tilde{a}^3 A^{\prime \prime}$ level of the HCF molecule. I know that the '3' in that expression refers to the multiplicity of that ...
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Linear combination of atomic orbitals (LCAO) justification for molecular orbitals (MO) done in this MIT solid state chemistry lecture
In this series on solid state chemistry by MIT, 11:00-13:00 in this lecture, LCAO for molecular orbitals is justified by the fact that Schrodinger's equation is linear (and therefore the superposition ...
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Question about "like dissolves like"
I know the rule of thumb of "like dissolves like". However, I'm not totally certain about the following scenario. Please check if my thinking is correct.
Suppose we have a non-polar molecule....
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Is really change in temperature inversely proportional to primary kinetic energy of ideal gas molecules?
I was trying to derive Charles law. While deriving I got two results and one of these was unexpected. Those are,
$$\Delta t \propto \Delta E_k$$
Where, $\Delta t$ is change in temperature and $\Delta ...
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Why does Hartree-Fock (HF) theory even work?
Let’s say we have $N$ electrons and we want to derive the Hartree-Fock (HF) equations. The first step would be to define a Slater determinant of $N$ electrons:
$$\psi(x_1,x_2,… x_N) = \frac{1}{\sqrt{...
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Why is there no exchange interaction when there is no coulomb interaction?
The Hartree-Fock energy may be written as
$$
E_{HF}= \langle\Psi| H |\Psi\rangle = \sum_{a} \langle a| h |a \rangle + \frac{1}{2}\sum_{ab} \big( [aa |bb] - [ab|ba] \big),$$
with the exchange term
$$[...
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Is the surface of a fluid more or less dense?
Paper explaining why surface tension is parallel to the interface:
Away from the surface there is perfect force balance due to the symmetry around a molecule. Near the interface, however, the up-down ...
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Surface tension of a fluid
I understand that there is an imbalance of forces between molecules that lie on the surface of a fluid compared to those that lie within. This results in the surface area is minimised. However, I can'...
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Underdamped and overdamped molecular vibrations
I am reading about the interactions between excitons and phonons in this article, and I came across the following equation for the underdamped component of the spectral density of the vibrational bath:...
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What was Laplace's argument?
In this Wikipedia article about Van der Waals gas equation there is a very nice derivation of the law in the conventional part. But in the last steps it is stated that pressure reduced on the walls of ...
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Energy of polyatomic molecular vibrations
I understand that the energies of a simple diatomic molecular vibration are equal to $E_n=(n+\frac12)\hbar\omega$, and I also know the accompanying eigenfunctions for these energies. I have also heard ...
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Molecular orbital basis mapping to computational basis
I have some issues understanding the process of mapping a molecular orbital basis onto some basis in a Hilbert space $\mathcal{H}$. As described in many papers (for example Simulation of Many-Body ...
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Energy of molecular vibrations
I have just read that the energy of a molecular vibration with frequency $\omega$ has eigenvalues of $(n+\frac12)\hbar\omega$, where $n$ is the quantum number. However, this equation really surprises ...
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Are number of molecules per unit volume constant (say in water)?
I have a very basic doubt. I knew that
$$ \rho = \frac{m}{V} $$
And since mass is constant so volume may decrease or increase depending upon density. But suppose I have water in a beaker and I read it ...
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Relevance of the Jahn-Teller theorem
Jahn and Teller stated in their paper that
All non-linear nuclear configurations are therefore unstable for an orbitally degenerate electronic state. Thus if we know of a polyatomic molecule that the ...
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If the melting point of Oxygen is -218 Celcius and the melting point of Hydrogen is -259 Celsius, why is the melting point of water 0 Celcius?
Forgive my ignorance, but my knowledge of Physics is not much, I am not even a High Schooler yet.
So, out of curiosity, I thought if water is H2O, 2 Hydrogen, and 1 Oxygen, then why is water's melting ...
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How does the phase and concentration affect the homo and lumo of materials?
We know the change in the Gibbs Free Energy is given by
$$ \Delta G=-nFE $$
and that the voltage is dependent on redox potentials which have to be between the homo and the lumo as max values. But what ...
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Does atomic particles have smell? [closed]
Do atomic particles like Sulphur or Hydrogen have their own distinct smell? Is the distinctive smell of Hydrogen Sulphide a combination of the smells of Hydrogen and Sulphur ? If not, then how do ...
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How is the HOMO-LUMO gap measured?
def:
HOMO = Highest Occupied Molecular Orbital
LUMO = Lowest Unoccupied Molecular Orbital
If the LUMO is unoccupied, how do we measure it? I can imagine that you can excite electrons in the HOMO but ...
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Absorption spectrum of open quantum systems
I'm trying to understand the properties of continuous absoption spectrum of molecules in a solution using an oversimplified quantum mechanical argument.
First, let us model our isolated molecule in ...
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Adsorption energy for physisorption
The adsorption energy describes the activation energy for adsorption and the desorption energy describes the activation energy for desorption. For only weak van der waals binding (physisorption) there ...
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Is it possible to analytically solve the Schrodinger equation for a single electron and multiple clasical nuclei?
It is well known that the Schrodinger equation rapidly becomes intractable as the complexity of the situation increases.
Solutions for a single quantum particle can often be obtained (depending on ...
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Rotational transition of a vibrational band of a CO$_2$ molecule?
I am currently reading this paper in regards to the lasing transitions of the CO$_2$ molecule:
https://journals.aps.org/pr/pdf/10.1103/PhysRev.136.A1187
Specifically, it keeps mentioning the ...
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What happens when you cool down a now closed container after the water evaporated in a open contained beforehand?
Imagine you heat up water in an open container until enough water vapor diffuses in the air. Then you stop heating the container, close the lid, and you cool it down. What happens next? This is my ...
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Why is the value of the heat capacity ratio $\gamma$ never less than 1?
For an monoatomic gas, the value of the heat capacity ratio $\gamma$ is 1.67
For diatomic gases, the value of γ (gamma) is 1.40
For many atomic gases, the value of γ (gamma) is 1.33
It's never less ...