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
1
vote
1answer
290 views

formation of σ molecular orbital in H2

In the picture, graphs show the constructive interference of two 1s atomic orbitals. My question is, what does the horizontal axis in wavefunction graph represent, does It represent the distance from ...
1
vote
1answer
312 views

Confusion about atomic/molecular orbital terminology

I have come across several different orbital terms: atomic orbitals, natural orbitals, split-localized orbitals, molecule-intrinsic orbitals, quasi-atomic orbitals. I don't know what the difference ...
1
vote
2answers
284 views

Heisenberg's Uncertainty Principle's inequality [closed]

In the uncertainty principle , whats the significance of the inequality sign ? Why is it not equal to over there ? Why do we say greater than equal to instead of just equal to ?
1
vote
2answers
9k views

Degenerate Orbitals

How do I know if an atom has degenerate orbitals? My Understanding I understand that degenerate orbitals mean orbitals that have the same energy level for the same n. However, how do I distinguish ...
1
vote
2answers
60 views

Relationship between Quantum Numbers and the Wave-function

I recently started learning about quantum mechanics and its applciations in atomic structure in chemistry. In this inorganic textbook Inorganic Chemistry, it describes "Each of the wavefunctions ...
1
vote
1answer
60 views

Why are s orbitals more “penetrating” than p orbitals?

In polyelectronic atoms, the reduction in the net central force due to electron-electron repulsion is accounted for through an effective nuclear charge that depends on a “shielding effect” of inner ...
1
vote
1answer
62 views

Electron configuration of non-hybridized carbon

I'm currently learning about orbital hybridization in carbon. I see that carbon has an electron configuration of 1s2 2s2 2p2. However, there are actually three p-orbitals in the second shell, namely ...
1
vote
2answers
101 views

Why does orbital optimization remove spin contamination?

I've come across numerous articles asserting that orbital optimized methods, where minimization of the energy is achieved through a series of unitary rotations (achieved by exponentiated single-...
1
vote
2answers
180 views

Effective nuclear charge and electron repulsion

To the best of my knowledge, the effective nuclear charge $Z_\mathrm{eff}$ is usually defined such that the potential energy of an electron in an atom, $\langle V \rangle$, can be expressed as $$\...
1
vote
1answer
54 views

exchange integral at large distances

I want to ask a question about the exchange integral $\ce{H_{AB}}$ - If I consider an exchange integral $\ce{H_{AB}}$ the following exchange integral can be evaluated: so $\ce{S_{AB}}$ is $0$ at $\...
1
vote
1answer
542 views

Atomic Orbital and Wave Function

I was reading about the atomic orbital in my chemistry textbook. It says that the atomic orbital (psi) is a mathematical wave function that depends on the coordinates of the electron. It is also ...
1
vote
1answer
422 views

Difference between Particle in a Box and Harmonic Oscillator approximations

Why in the particle in a box model do the values of n begin at 1 but in the harmonic oscillator they begin at 0? I understand what the wave-functions and their corresponding probabilities look like ...
1
vote
2answers
80 views

Perturbation Theory in Orbital Interactions in Chemistry

In the entire book, perturbation theory is used as a qualitative tool to rationalise some chemical phenomena. The authors write that $$\psi_i = \sum_\mu{T_{ji}\psi_j^\circ}\tag{1}$$ The proof of the ...
1
vote
1answer
275 views

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 ...
1
vote
2answers
111 views

Why is nucleus charge squared in Rydbergs formula?

According to coulumbs law, the energy changes linearly with charge. So why is the nucleus charge squared in this formula? Is there a way to derive it? I was suspecting it might be because it pulls ...
1
vote
1answer
59 views

Molecular Orbital Mixing to get the Molecular Orbitals of a large molecule

I am trying to get the molecular orbital for arbitrarily placed nuclear centres (identical). In other words , I am trying to solve the following one electron hamiltonian. $$h=-\dfrac{1}{2}\nabla^{2}-\...
1
vote
1answer
217 views

What exactly is a potential energy surface?

I first learned about potential energy surface (PES) when I was studying Born-Oppenheimer approximation. In the approximation, the PES is essentially electronic PES which is defined as follows: ...
1
vote
1answer
303 views

Is there a simple way to predict the molecular pi orbitals in conjugated pi systems?

Particularly for longer alkyl chains. Or is predicting these molecular orbitals from quantum mechanics too complex to be able to be translated easily as a geometric pattern? If Frost Circles exist, I ...
1
vote
1answer
160 views

Why does aqeous fluorescein shine when exposed to UV light?

I know that (aq) fluorescein "absorbs" UV light and releases light in the visible spectrum , but how does it do that. It is a really interesting and useful organic chemical and I just wanted to know ...
1
vote
1answer
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 ...
1
vote
1answer
77 views

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

Can the eigenvalue for a quantum mechanical operator be zero?
1
vote
1answer
797 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?
1
vote
2answers
799 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? $...
1
vote
1answer
803 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 ...
1
vote
1answer
475 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 ...
1
vote
1answer
290 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 ...
1
vote
1answer
503 views

Radical Computational Calculations [closed]

I am trying to calculate the total energies for a particular organic molecule that undergoes radical decomposition. I was able to calculate the neutral molecule with the exact results of a paper I ...
1
vote
2answers
812 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 ...
1
vote
1answer
43 views

Could observer effect cause electrons in one orbital to be found in another?

The observer effect states [1] that when unobserved, absolutely small particles like electrons can simultaneously be in two different states at the same time. If we look at an atom of any element, ...
1
vote
1answer
46 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 ...
1
vote
1answer
207 views

What are the steps of Hartree-Fock Theory?

Outline the steps involved in the Hartree–Fock method for the calculation of molecular electronic structure. I understand the basics of HF, in that it does not account for electron correlation (...
1
vote
1answer
178 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 ...
1
vote
1answer
59 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 ...
1
vote
1answer
2k 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 ...
1
vote
1answer
146 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 ...
1
vote
1answer
163 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 @...
1
vote
1answer
97 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 ...
1
vote
1answer
535 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^...
1
vote
1answer
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 ...
1
vote
1answer
352 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). ...
1
vote
1answer
276 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 $\lambda=1/k$ ...
1
vote
1answer
242 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 ...
1
vote
1answer
55 views

What's the meaning of wavefunction being finite?

I know ,in quantum mechanics it's important that the wavefunction has to be finite everywhere , including infinity. It's a criteria for acceptable wavefunction . What exactly does this statement mean ?...
1
vote
1answer
34 views

Radial wave-functions and spherical harmonics of p-orbitals in a certain hypothesis

I know that the s-orbitals of H atom are spherically symmetrical. But the p,d or f orbitals aren't. So, the H-atom needn't necessarily be spherically symmetrical, as the wave-function would be a ...
1
vote
1answer
46 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 ...
1
vote
1answer
101 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 ...
1
vote
1answer
69 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). ...
1
vote
2answers
87 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 ...
1
vote
1answer
75 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 ...
1
vote
1answer
167 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 ...

1
18 19
20
21 22
26