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, ...).

Filter by
Sorted by
Tagged with
0
votes
2answers
87 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 ...
0
votes
2answers
87 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 ...
0
votes
1answer
941 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 ...
0
votes
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.
0
votes
1answer
78 views

What does Pauli’s exclusion principle mean in atomic or fundamental way? [closed]

It means is that no electron can have same n , l and $m_l$ but can have two different spin quantum number. I want to know why is this rule valid?Means there must be some other things happening also ...
0
votes
1answer
98 views

How can an electron being a wave have such property as spin?

Here's what I know about electrons. Electrons have wave-like properties and the number of wavelengths in the $n^\text{th}$ shell is equal to $n(\lambda).$ Also, I read in my book that they have ...
0
votes
1answer
143 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}...
0
votes
1answer
188 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.
0
votes
1answer
78 views

Classically permitted position values in a quantum harmonic oscillator [closed]

In a quantum harmonic oscillator that is in the state with quantum number $n$, what range of the position $x$ is allowed classically? Does it have something to do with Bohr's correspondence principle?...
0
votes
1answer
60 views

What is the form of the Hamiltonian for solids?

For atoms, and even molecules, I can understand how the Hamiltonian would be constructed, but what of solids (as in, for electronic structure calculations)? Thank you for any help.
0
votes
1answer
68 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-...
0
votes
2answers
281 views

Is this what an orbital means?

In this picture, there is a $1s$ and a $2s$ orbital. Are the orbitals only the dark gray circles ? Or are the light gray circles (which are surrounding the dark gray ones on both sides) also included ...
0
votes
1answer
1k 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-...
0
votes
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 $\ce{F-}$?
0
votes
2answers
55 views

Why is the radial distribution at the nucleus 0 but not the radial wave function?

The modulus squared of the radial wave function gives the probability of finding an electron in an infinitesimal volume dv. On the other hand, the radial distribution gives the probability of finding ...
0
votes
2answers
853 views

Binding energy vs. ionization energy [closed]

I am studying binding energy in the context of photoelectric spectroscopy, and I came across a graph of relative numbers of electrons vs binding energy (in units of megajoules per mole). The element ...
0
votes
1answer
69 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, ...
0
votes
1answer
57 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, $\psi_{(r,\theta,\phi)}=R_{(r)}Y_{(\theta,\phi)}$...
0
votes
1answer
59 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?
0
votes
2answers
142 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 ...
0
votes
2answers
140 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 $\...
0
votes
1answer
52 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 ...
0
votes
1answer
101 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 $...
0
votes
1answer
3k 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 ...
0
votes
1answer
397 views

Thermal and photochemical excitation of electron in photochemistry

One of the basic rules of photochemistry is that the electronic configuration of a conjugated polyene does not change when excited thermally, but changes when photochemically excited, i.e. an electron ...
0
votes
2answers
134 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. ...
0
votes
1answer
56 views

The quantum mechanics behind periodicity of elements

Especially in high school/first-year undergraduate chemistry courses, we learn with great dedication the periodicities along groups and periods. There are various useful and interesting trends. I ...
0
votes
1answer
45 views

nodes and probability density

The square of the wavefunction gives probability density of finding an electron somewhere in the orbital. The text I'm referring to says that the value of probability density is always higher than ...
0
votes
1answer
66 views

Proof for second-order perturbation term of energy

In perturbation theory, if \begin{align}{\hat {H}} &= {\hat {H}^{(0)}} + λ{\hat {H}^{(1)}} \tag{1}\\ {ψ} &= {ψ^{(0)}} + λ{ψ^{(1)}} +λ^2{ψ^{(2)}} + ... \tag{2}\\ {E} &= {E^{(0)}} + λ{E^{...
0
votes
1answer
177 views

How to calculate Hirshfeld charges from Gaussian?

I am new to Gaussian and want to calculate Hirshfeld charges from Gaussian 09 or 16. I found this input file for Methanol: ...
0
votes
1answer
35 views

Wave function of a perturbed system

In perturbation theory, wave function of a perturbed system can be expressed in a power series of some $\lambda$ as $\psi^{(0)} + \lambda\psi^{(1)}+\lambda^2\psi^{(2)}......$. Then we express ...
0
votes
1answer
51 views

Expectation value of an observable in quantum system

In quantum systems, sometimes if the wave function is not an eigen value of an operator then it is expanded in terms of bases states, then we apply the operator over the bases states and we get ...
0
votes
1answer
46 views

What's the definition for mole before Avogadro's constant?

I have been searching for about 3 days how Avogadro's constant is found, and as all of us know the value is determined by division of charge of one mole of electrons (Faraday's constant) by the charge ...
0
votes
1answer
39 views

Normal modes of vibration [closed]

Why Normal modes of vibration are important when compared to translational and rotation modes. And why the frequencies for rotational and translational modes are close to zero?
0
votes
1answer
41 views

Photoelectric effect with 0 Kinetic Energy?

Does the photoelectric effect take place if the frequency of the photon is exactly equal to the threshold frequency of the metal? I know the electron is going to be free, but it will have 0 kinetic ...
0
votes
1answer
72 views

Getting the pressure of a system by series expansion

An average number, $N$, of bosons of spin $S = 0$ is conned to a two-dimensional domain with surface $A$. The gas is ultrarelativistic with a single particle energy $\epsilon = cp$, where $c$ is the ...
0
votes
1answer
64 views

According to MO theory, do 1s orbitals in dioxygen interfere?

According to MO theory, are the 1s orbitals in $\ce{O2}$ too radially contracted to interfere with each other and thus cannot form bonding and antibonding orbitals, or do they still do that?
0
votes
1answer
288 views

Effective nuclear charge on an inner electron

Is the shielding effect in a multi-electronic species caused due to mutual repulsion of electrons? If it were so, while calculation the $Z_\text{eff}$ on an electron in say the $\mathrm{2p}$ orbital ...
0
votes
1answer
22k views

Energy of an electron (why negative?) [duplicate]

Why is the energy of an electron in an orbit is always negative? What does it mean? Why isn't it positive? Does it mean that energy is released by revolving electron?
0
votes
1answer
424 views

Spin of electrons about it's own axis, release of energy & COLLAPSE of atom? [closed]

An electron spins about it's own axis. So it has rotational accln. Thus, according to Maxwell's Electromagnetic Theory , Rotational Kinetic energy must be released. Thus, at some pt. of time , ...
0
votes
1answer
60 views

How to find probability in different basis representations?

The matrix representation of the Hamiltonian is given in the position basis: $\{|+a\rangle,|-a\rangle\}$. $$H = \begin{pmatrix} E_{0} & E_{-A} \\ E_{-A} & E_{0} \end{pmatrix}$$ The initial ...
0
votes
1answer
250 views

installation error of dalton 2015 in ubuntu 12 [closed]

what are the answer for CONFIRMATION OF REGISTRATION when register in dalton forum ? install got error, how to install dalton 2015 wonder@wonder-VirtualBox:~/dalton/DALTON-Source$ uname -r 3.8.0-...
0
votes
1answer
187 views

Subtle implications of quantum numbers

Question: Given the subshells $\ce{1s, 2s, 2p, 3s, 3p}$ and $\ce{3d}$, identify those that meet the following descriptions: a) has $l=2$ b) Can contain two electrons with spin $m_{s}=\pm\...
0
votes
1answer
2k views

How to identify ions by their quantum number?

If the quantum numbers of an ion are given, how can we identify this ion by its quantum numbers? For example : n = 3; $l$ = 2; $m_l$ = 0; m$_s$ = + ½ What I have so far: $n$ is 3 and $l$ is 2 ...
0
votes
1answer
109 views

What exactly happens to mass during deuterium fusion?

I know that the mass of Helium-4 is slightly less than the mass of 2x Deuterium it may be made of and that it is the reason fusion gives a lot of energy. But where exactly is this missing mass taken ...
0
votes
1answer
51 views

Schrodinger's Equation and Wave Function

So I understand that there exists the shrodinger's equation, which on solving,gives the wave function of an electron. The wave function as I understand, gives all possible information about an ...
0
votes
1answer
120 views

Why does the energy level of a particle in a box decrease with length?

I want to know the intuition of why L is in the denominator of the equation for the energy of a particle in a box. This helps explain why resonance is stabilizing without using molecular orbitals. ...
0
votes
1answer
68 views

Computational chemistry software to generate files of cartesian coordinates and zmatrix of molecules

Is there any software that I can provide bond lengths, bond angles and torsion dihedrals of a molecule and generate an output file in the format of cartesian coordinates or zmatrix? Example: I would ...
0
votes
1answer
37 views

How do orbitals overlap in difluorosilane? [closed]

In $\ce{SiH2F2}$ four orbitals of silicon $(\mathrm{3s},$ $\mathrm{3p}_x,$ $\mathrm{3p}_y,$ $\mathrm{3p}_z)$ overlap with two hydrogen $(\mathrm{1s})$ and two fluorine $(\mathrm{2p}).$ I want to know ...
0
votes
1answer
46 views

What is the reason that ice melts with increasing pressure at constant temperature (revelation)?

I've seen many explanations regarding this topic where they explain it in the sense of the anomalous expansion of water, but I actually want an answer where I can understand the different forces at ...