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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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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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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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 ...
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116 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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176 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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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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103 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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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 ...
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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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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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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 ...
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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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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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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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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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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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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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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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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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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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357 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 ...
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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. ...
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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 ...
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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^{...
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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: ...
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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 ...
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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 ...
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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 ...
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38 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?
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35 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 ...
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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 ...
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62 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?
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278 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 ...
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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?
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396 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 , ...
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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 ...
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248 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-...
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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\...
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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 ...
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107 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 ...
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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. ...
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55 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 ...
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1answer
36 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 ...
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37 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 ...
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53 views

Why can a wave-function be written as a product of 1-electron wave-functions?

Why can a wavefunction be written as a product of 1-electron wave-functions when making approximations to solve atoms other than hydrogen? (ie. helium) We used this when solving multielectron systems ...
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94 views

Software that determines whether a molecule can exist and draw it from a formula?

I have run calculations that predict atomic configurations. As a simple example, in a system that contains H and O, I might get a list like: ...
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63 views

Ab Initio and Molecular Orbitals [closed]

What is the difference between ab initio calculations and molecular orbital theory?
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61 views

How does increasing temperature reduce the efficiency of solar cells?

I've seen several answers and trying to confirm. 1) Does temperature increase the ground state energy of electrons once they reach the positively doped semiconductor, thus reducing the voltage ...
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110 views

Van der Waals interaction and magnetic dipole dipole interaction

I have a conceptual question that bothers me. From what I understand, van der Waals forces are the primary source of inter-molecular interaction. There are three different possible origins for van ...
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1answer
1k views

What is the relationship between the values of n and ml? [closed]

Example question: ml=+5 what is the lowest value of n? I can't seem to remember the easy trick to finding the relationship if someone could explain that would be great. -Thank you in advance.