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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64 views

Implication of completely non relativistic Hamiltonian

I am studying the Application of perturbation theory to hydrogenic atoms subject to internal or external electromagnetic fields. The very first equation it uses is the hamiltonian of hydrogenic ...
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74 views

Can the eigenvalue for a quantum mechanical operator be zero? [closed]

Can the eigenvalue for a quantum mechanical operator be zero?
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1answer
766 views

Role of nodes in stability of orbitals

What role does the node play in determining broadly the relative stability of various types of atomic orbitals with the same principal quantum number?
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764 views

Why does a photon have linear momentum, although it doesn't possess mass? [closed]

We know that photon doesn't possess mass. But it has a tendency of colliding with surfaces, as we see in the photoelectric effect. As it doesn't possess mass, then how does it have linear momentum? $...
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741 views

What is the basis for naming the p-orbitals with reference to the Cartesian coordinate system as x, y, and z?

There are 3 p-orbitals per subshell, which are $p_x$, $p_y$ and $p_z$. As well as there are 5 d-orbitals, which are $d_{xy}$, $d_{yz}$, $d_{zx}$, $d_{x^2-y^2}$, and $d_{z^2}$. My Question: What is ...
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1answer
428 views

What is the reason why protons and electrons do not collide?

can someone give me an intuitive picture of why electrons don't collide with protons? I know that electrons move in a sort of cloud, which is our 'orbital', and that they mainly behave like ...
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1answer
286 views

Nuclear zero-point energy and quantum delocalization effects of water molecules

What do we mean by "Nuclear zero-point energy" and "quantum delocalization effects" of water molecules ? It's said that without these effects "water" becomes somewhat unbounded, which is not very well ...
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2answers
801 views

Is probability of finding electron changing here?

We all know what is a wave function. There is a technique to convert non normalized wave function to normalized wave function. In case of non normalized wave function integration of square of wave ...
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1answer
44 views

Explanation of terminology in equation used for energy calculation using Hartree–Fock method

I found in the literature that the energy of the Hartree–Fock method is given by the following equation: $$E_\mathrm{HF} = \int (\Psi^* \hat{H}\Psi)\,\mathrm d\tau$$ The term $\Psi$ is the wave ...
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2answers
210 views

What is the relationship between entropy and heat capacity?

The molar heat capacity of hydrogen gas and deuterium gas are nearly the same, 28.8 J/K mol and 29.2 J/K mol respectively, but the absolute entropy of deuterium (145.0 J/K mol) is significantly larger ...
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148 views

What does ³D mean in energy level diagram for helium?

I'm coming from a Physics background and am trying to make sense of the energy level diagram for para-helium and ortho-helium. From what I've gathered each column shows the different energy levels ...
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1answer
57 views

What all information can be gathered qualitatively from the radial distribution functions of a molecule?

Apart from knowing the radius of coordination shells and the probability of finding, is there any other thermodynamic information we can gather by looking at radial distribution functions of a ...
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1k views

Radial Probability Distribution Curve versus ψ² versus r curve for 1s orbitals

My question is basic, but I have already referred to a couple of books. This is an excerpt from Linus Pauling's book: the most probable distance of the electron from the nucleus, which is the ...
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1answer
139 views

Quantum mechanical model of atom

While going through the quantum mechanical model of atom section in my chemistry textbook, the text states: The existence of quantized electronic energy levels is a direct result of the wave-like ...
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1answer
155 views

How have I to understand in what those quantum numbers refer for ortho and para water?

I need to make an English presentation at my School (Graduate school) about something people may don't know. I chose to speak about the separation of ortho and para water. I first chat here with @...
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1answer
92 views

Supramolecules in Spartan

Maybe someone here is familiar with supramolecules calculations using Spartan? I am new in this area and trying to figure out some things: First - what's the best way to draw them? I tried to draw one ...
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526 views

A question about exercise 2.1 in Szabo and Ostlund's modern quantum chemistry, namely inner product between different spin orbitals

I feel quite confused about this question. Consider the spin-orbital integral $$\langle \psi_I^{\alpha} \alpha (\omega) | \psi_J^{\beta } \alpha (\omega) \rangle = \langle \psi_I^{\alpha} | \psi_J^...
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25k views

How many electrons can have the quantum number set n=5, l=3, ml=-1? [closed]

How many electrons can have the quantum number set $n=6,\ l=3,\ m_l=-1$? Also, please explain why. I know that n describes the number of shells in an atom but what do n, l, and ml have to do with ...
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330 views

What are the molecular orbitals of the hypothetical linear H₃⁺ molecule?

What would be the wave function of the lowest energy molecular orbital of a hypothetical linear H3+ molecule? According to the LCAO method, I feel the lowest energy MO will be 1s(A) + 1s(B) + 1s(C). ...
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1answer
269 views

Two-electron Integrals over Gaussian Plane Waves [closed]

Is there an efficient method to compute the two-electron integrals over the basis set represented by a product of a Gaussian function $g(r)$ and plane wave: $\psi(r)=g(r)e^{ikr}$ where $\lambda=1/k$ ...
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1answer
241 views

Bonding, multiplicity and quantum chemistry for FeP2

I’m trying to do some quantum chemical calculations for the linear molecule $\ce{FeP2}$ in the gas phase as well as its crystal (orthorhombic symmetry like here). I am lead to believe that in both ...
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1answer
37 views

Regarding the probability density of finding an electron in between a bond

I'd found the image attached on a website explaining the molecular orbital theory. My question is, shouldn't the graph have a maximum at the middle of the two hydrogen atoms? since my intuition tells ...
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1answer
80 views

What does orbital mean, exactly? [duplicate]

My teacher told me that orbital is the probability distribution data of the electron around nucleus which is amplitude data in a way. An example of how my teacher actually told what it means involves ...
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1answer
41 views

Do changing opt=modredundant to opt in Gaussian makes geometry optimization not to take into account frozen angles?

I am a newbie to Gaussian and just generated an input for the geometry optimization for some molecules with multi ring system. However, in the article that was a reference for those calculations, some ...
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1answer
59 views

Spin orbital coupling and total angular momentum

The Sodium emission spectrum has 2 bright yellow lines called the Na-D lines. Superficially I understand the cause; there's spin-orbit coupling and the 3p orbital is split into 3p(3/2) and 3p(1/2). ...
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2answers
81 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 ...
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1answer
66 views

Rotational Energy Levels

Why does the rotational constant B decrease and transition spacings decrease as the mass of a particle increase? I understand from a purely equation perspective that since $$B = \frac{h} {8\pi ^2 ...
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1answer
152 views

Molecular dynamics (Mac OSX user): what software can I use to plot RDFs for NPT simulations? VMD only works for NVT (constant volume)

I would be very grateful if someone could recommend a way to plot RDFs for NPT ensemble molecular dynamics simulation results. I use CP2K to run NVT simulations and usually use VMD to process ...
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1answer
97 views

Interaction of the oscillating magnetic field of electromagnetic radiation with a molecule or atom

Whenever we read rotational, vibrational and electronic spectroscopy, we find details on the interaction of the electric dipole moment of the molecule with the oscillating electric field of ...
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1answer
218 views

Molpro - Connection between atomic term symbols and system symmetry

Let's say I have a carbon atom with the electron configuration $1s^22s^22p^2$. We know, that using atomic term symbols we can describe the following states: $${}^3P_0, {}^3P_1, {}^3P_2, {}^1D_2, {}^...
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1answer
108 views

Wave-particle duality in electron [closed]

Electrons show wave-particle duality Particle (atom) containing a wave (electron) on Quora Atoms contain electrons. We consider atoms as particles but electrons which are inside the atom as waves (...
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1answer
801 views

Why do the 4f and 5d orbitals have similar energies?

I've come to know this phenomena when learning about the exceptions to the aufbau principle. But there is no explanation of why 4f and 5d have similar energies (as I've read in some websites).
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695 views

How does the screening effect work for orbital in the same shell?

Energy of an orbital in a single electron system depends solely on n, while energy of orbital in multi electron system depends on n and l, why is that? I understand that the screening effect is at ...
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1answer
49 views

Is it possible to define the coordinates of an atom using other coordinates while optimizing in gaussian 16?

I know it is possible to fix the value of composite expressions using generalized internal coordinates (gic) in gaussian 16. But is it possible to assign that value to the coordinate of another atom. ...
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1answer
82 views

Does the probability function for a molecule to have energy in a certain mode depend on the minimum required quantum energy level of that mode?

I understand that the probability density for a particular velocity v+dv in one dimension for a molecule in a system is: $$f(v) = \sqrt{\frac{m}{2\pi k_B T}} \cdot e^{\frac{-mv^2}{2k_B T}}$$ I'm ...
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1answer
436 views

Radial probability for orbitals [closed]

Questions Question F-2: I think question f1 requires one to relate $\mathrm{\psi^2}$ or. Probability density with radius but I am just in high school and have not learnt about Hamilton ...
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1answer
422 views

Do atoms in a molecule actually keep rotating freely in case they have sigma bond? [duplicate]

While reading about cis-trans isomers I found the concept of free rotation of atoms.it says 2 atoms connected by sigma bond do not have trans sis isomer because of free rotation.while in case of pi ...
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1answer
149 views

Balmer's formula and lagurre polynomials [closed]

How can you explain the Balmer's formula using the properties of Laguerre polynomials? It's a homework question but I really don't get it. 1.What is the property of the Lagurre polynomials in the ...
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1answer
187 views

PIB wave functions and the effects of e- delocalization on UV absorption in conjugated systems

I'll try to keep this short and concise. What made me start thinking about this question was the material we have been covering regarding PIB wave functions in my quantum chemistry class, and material ...
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1answer
1k views

Why does greater orbital overlap mean a stronger bond?

According to valence bond theory, orbital overlap produces a bond. However, I don’t understand why having greater orbital overlap renders a bond stronger. It’s intuitive, I suppose, but I haven’t been ...
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1answer
446 views

Does a wavefunction have to be an eigenfunction of an operator in order to obtain an expectation value?

I am reviewing an intro quantum chemistry book and I came across the line "If $\hat{A}$ corresponds to a physical property of the system, whether or not $\psi$ is an eigenfunction of $\hat{A}$, the ...
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1answer
448 views

Why are wavefunctions with same principal quantum number and different azimuthal quantum number orthogonal

The value turns out to be zero . This is understandable since they are completely independent of each other and also perpendicular in real space. But also turns out to be zero . How do I justify the ...
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1answer
85 views

Ignoring spin, consider an electron in a hydrogen 2p orbital, what is its orbital magnetic moment?

I know that a magnetic dipole moment is given by $$\mu=\frac {-e}{2m}I$$ and that the z component of angular momentum is $$m_j\hbar.$$ However, I have also seen that angular momentum $I$ is given by $$...
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1answer
111 views

Conical intersections - phase

Can anyone explain why at a conical intersection the wavefunction changes sign? My understanding is that it is a test to see if the crossing IS indeed a conical intersection or just a coincidence of ...
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77 views

What causes little spikes in a flame? [closed]

I have a lighter at home which everytime I use it, generates little spikes (see picture below) which eventually disappear. The Spikes are not an effect generated by the camera. I can confirm that ...
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How to calculate core electron SCF Fock Matrix Elements?

I have searched everywhere but there are no worked examples of how to calculate the $\langle\chi_i |\hat{h}| \chi_j \rangle $ values for the Fock Operator using the SCF HF Roothaan method. I am given ...
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1answer
51 views

Do different eigenstates of total angular momentum have necessarily different energies?

Let $H$ be the Hamiltonian of a specific atom and $J$ the total angular momentum. Since $H$ and $J$ commute, they have common eigenstate. So we can label the atomic states by their energy and total ...
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1answer
40 views

Why does the Most Stable State of an Atom Tend to be One with Full s and p Subshells?

I'm new to posting on stack exchange, although I've read a lot of it before. This question seems like it might end up being marked as a duplicate, but I've looked through a lot of the similar ...
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61 views

Comparison between Molecular Orbital Theory and Valence Bond Theory

I have been reading about introductory Molecular Orbital Theory lately. Till now, I have used Valence Bond Theory to evaluate bonding. I have a few questions about it:- In VBT, we used the idea that ...
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42 views

Exchange energy

The half filled and full filled configuration is considered to be most the stable among the other configurations. But d7 or d8 configuration has a greater exchange energy mathematically. So why isn't ...

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