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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In 1 dimension, the curvature of Ψ = K.E. of wave. Is this the case for 2 dimensions and 3 dimensions also?

In 1 dimension, the curvature of Ψ = K.E. of wave. Is this the case for 2 dimensions and 3 dimensions also? Moreover, is curvature of Ψ = K.E. of wave = 2nd derivative of Ψ?
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What is the intuition of using “dimer method” for searching transition states?

I learned dimer method for searching transition state in this paper: A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives. However, I still ...
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768 views

Calculation of average bond length from force constant and IR absorption?

I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself). The problem gives me the IR absorption for a diatomic, as well as the force constant for the ...
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59 views

Is the energy of the orbital an electron “resides” in, considered to be a factor of that electrons ionization energy? [duplicate]

The answers to a Quora question mainly refer to the factors as generally being, the electrostatic forces of attraction between the electron and the positively charged nucleus and all other events, by ...
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241 views

The nature of Chemical Bonds [closed]

It was nearly a year ago when I appeared for my first interview through the KVPY (a research oriented scholarship exam) when one of the questions the panel asked me was : What is a chemical bond? I ...
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38 views

How on the quantum level do the notch filters used in Raman spectroscopy remove only a select wavelength of light?

From what I have gathered regarding the schematics of Raman spectrometers, the notch filter is used to remove a narrow range of light corresponding to that of the laser used to excite the sample. How ...
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49 views

Probabilities of Electrons in Orbitals [duplicate]

I've heard both of the following: An orbital is a region where there's a 90% probability of finding an electron An orbital is a region where an electron spends 90% of its time Are these essentially ...
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224 views

Quantum Mechanical Model of An Atom, Shells, Subshells [duplicate]

I've just been introduced to the quantum Mechanical Model of an Atom, so please bear with me on this one. Are Subshells and shell physical things, like do they really exist, or is it a concept only to ...
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Difference between Covalent and non-Covalent interactions

It is a general concept that non-covalent interactions are a result of electrostatic interaction while covalent interactions arise due to sharing of electron density. This, however, is not true since ...
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177 views

Why must the ground state of hydrogen molecule be gerade?

As we know, the electronic ground state of hydrogen molecule is $\Sigma_g^+$. My question is, how do we know it from the theoretical perspective? The nuclear potential in the hamiltonian of hydrogen ...
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36 views

rovibrational spectroscopy: why do intensities of rotational lines increase with J? [closed]

how and why do the intensity of rotational lines change with J value? in the simplest terms possible please
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How does the electron configuration correlate with the emission spectrum of an ionic compound? [closed]

trying to find a way to correlate the electron configuration of an ionic compound (ie. Cupric sulfate, potassium chloride, Cupric chloride, sodium carbonate, strontium chloride) with its emission ...
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Nodes of orientation of electron orbitals [duplicate]

As you can see the orientation of 2 p orbital there is a nodal plane in between the electron density pictures.... So doesn't the electron move from left to right side in2 p X orbital. I think that ...
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84 views

Should the normal mode of vibration leading to the transition state be removed?

I would like to know whether the normal mode of vibration of the reactant should be deleted when calculating $\Delta ZPE$ and $\delta G_{\text{corr}}(T)$, where $\Delta ZPE$ is the zero-point energy ...
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57 views

How to determine which normal mode leads to the transition state (numerically)? [closed]

I would like to get the normal mode of vibration which leads to the transition state. Do you know any software for this problem? If no, could you offer an algorithm to generate it? By the way, is ...
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What is meant by 'penetration of atomic orbitals'? [duplicate]

While studying atomic structure, I have faced this term very often. I assume this is a very detailed type question! But if anyone can please provide just the preliminary idea about this, it will be ...
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how to understand to what subshell is related basis function in the Eigenvectors block (GAMESS output)?

So, each subshell of some atom is described by one or combination of few BF's. But I can't find correlation between representation of subshells in eigenvectors block and, say, basis set or something ...
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91 views

Spatial form of an atom and type of chemical bond

As we know, the first excited states of Hydrogen atoms is $2p$. The wave functions in cartesian basis we can represent as $$ p_x = \frac{1}{\sqrt{2}} \left( Y_{1, +1} + Y_{1, -1}\right) =\...
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What is the significance of increasing (and decreasing) the number of ionic releaxation steps in a plane wave DFT calcuation? [closed]

The number of ionic relaxation steps is one of the adjustable parameters while setting up a DFT calculation using a commercial code such as VASP. I was wondering what's the significance of this value?
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45 views

quantum capacitance of supercapacitor electrodes, high or low needed?

quantum capacitance of supercapacitor electrodes should be low or high? to achieve high specific capacitance. The quantum capacitance forms among the layers of low DOS materials when used as an ...
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112 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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57 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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480 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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233 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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345 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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615 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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37 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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52 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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169 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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325 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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372 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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91 views

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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1answer
2k 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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1answer
987 views

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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18k views

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
62k 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
1k 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
801 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
132 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
145 views

Why do 1s and 2s orbitals intersect? [closed]

So I was going through the Schrödinger wave equation to determine the shapes of orbitals. We know that an orbital is nothing more than a region where probability of finding an electron is maximum. ...
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1answer
89 views

Is the pz orbital wave function three- or four-dimensional?

The wave function of the $2\mathrm{p}_z$ orbital is $$Ψ = \frac{1}{4\sqrt{2π}}\left(\frac Z a\right)^{5/2} r \mathrm e^{-Zr/a}\cos θ.$$ I'm confused if this function will be a three-dimensional ...

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