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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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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Why can’t every element emit all the colours from the emission spectrum [closed]

If there is an infinite number of levels, this means that every electron can jump from as many variations as possible. Hence, why can’t every element emit every colour? Please don’t use very ...
62 views

Atoms visualisation [closed]

In 7th class I was been taught that in an atom, electrons revolve around shells and the electrons with higher energy level are placed likewise in the shell above of that electron: In 11th class I ...
38 views

metal ion complex with carbon dioxide [closed]

Using ORCA and Avogadro, I stimulated the possible MO orbitals of carbon dioxide complex with lithium ion (Lithium chloride) and cesium ion (cesium chloride) each at a time. i expected that Due to ...
33 views

Diagrams for the wave functions [closed]

I came across a question in one of the papers of JEE Advanced, which i didn't understand. The question is as follows: $P$ is the probability of finding the $\mathrm{1s}$ electron of hydrogen atom in ...
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Effective core potential and Gaussian basis set

Is using the effective core potential (ECP) and Gaussian basis set simultaneously in ab initio calculation a valid approach? For example, is it correct to use ECP for one of the atoms and, instead of ...
63 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 ...
33 views

Evaluation of an element of a basis function and its derivative using some chemistry package [migrated]

Given some element and one of the basic functions of one of the Gaussian basis sets, I'd like to be able to recover the maximum value any of the basis functions can take, as well as their maximum ...
56 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 ...
986 views

Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?

I am trying to figure out how is it possible to reconcile the reality of exothermic reactions, which means that kinetic energy is transferred to (heats) the surrounding matter, with the principle of ...
45 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. ...
50 views

Analytic Hessians for meta-GGA functionals [migrated]

In many of the free/open-source QM programs like GAMESS, ORCA, NWChem, the calculation of analytic hessians is not possible when a meta-GGA density functional is used, like M06-2X. My first question ...
72 views

Negative s - orbital chatacter

I am learning about how to calculate s-orbital character. While doing so, I came across a formula $$\cos\theta = \frac{s}{s-1}.$$ For cycloproprane, I used $\theta = 60^\circ,$ and got $s = -1.$ How ...
24 views

Potential energy surface in transition state theory

I would like to study the typical reaction from the transition state theory: $$\ce{AB + C <=> ABC^‡ -> A + BC}$$ Assuming $\ce{ABC^‡}$ is a colinear molecule, the potential energy surface of ...
57 views

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How would you know if the light emitted is of one wavelength or if it is a mixture of two or more wavelengths? [closed]

I am just learning some chemistry after a long time without studying it and I have thought about something. Some copper compounds emit green light when heated to flame. So, I would like to know if it ...