# 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, ...).

1,414 questions
Filter by
Sorted by
Tagged with
1 vote
27 views

### Probability density and radial distribution function of finding the most probable distance of electron in 2p orbital in hydrogen atom

Referring to the answer by DSVA (Most probable point for finding an electron in the 1s orbital of a Hydrogen atom) There's a maximum of finding the electron at a certain distance away from the core (...
18 views

### How can I drive Heisenberg's uncertainty principle from the wave function [closed]

I want to find Heisenberg's uncertainty principle from the wave function.
66 views

### Violation of pauli's exclusion principle? ( During formation of neutron star or black holes) [closed]

Sorry it's a bit long so i was watching Action labs video on how neutron stars are formed and in that he says " if there's enough mass, then the mass will keep on collapsing in on itself in the ...
102 views

### Proof for equation of radial probability distribution curve

So my textbook says the equation for this is $$P(r) = 4\pi r^2\Psi^2$$ It also gives the volume of the shell formula $$\mathrm{d}V = \frac 43 \pi(r+\mathrm{d}r)^3 - \frac 43 \pi r^3$$ which I ...
30 views

### How do I show that a transition is electric dipole allowed with group theory/symmetry?

This is actually a follow up of this question The follow-up is not because of the electric instead of magnetic dipole (this is trivial). It is because I'm interested in extra info. Suppose I have a ...
88 views

### If two atoms join, do they lose their original spectral lines? [closed]

Each element and even isotope of element has its own set of unique spectral absorption lines. What happens to these lines after two or more atoms join together into molecule? Are all of the lines that ...
75 views

### Which quantum numbers does the orbital angular momentum depend on? [closed]

I learned from a question that I recently solved that the orbital angular momentum depends on both the azimuthal and magnetic quantum numbers. I did not expect this because the formula for the orbital ... 1 vote
66 views

### Estimating the energy required for dissociation from visible absorption spectra

I have been having trouble solving the following problem. The question calls for an estimation of the energy (in kj/mol) required to dissociate ClO in its excited state when it is excited from the v = ...
31 views

### Interpair vs. intrapair nondynamic correlations

What is the difference between interpair and intrapair nondynamic correlations? What would an example of each “look” like in the context of the $\ce{H4}$ system ? Reference Ramos-Cordoba, E.; ...
1 vote
17 views

### Modelling barrier-less reactions

I am currently exploring a few dissociative reactions whose PES is barrierless (no first order saddle point). I have found a few approaches in literature like flexible nudged elastic band theory, ...
50 views

### Is Lennard-Jones potential "abused"?

Bond Formation For example, when describing the potential energy curve of hydrogen molecule, the Lennard-Jones potential is employed and the energy minimum corresponds to the bond length of the ...
1 vote
6 views

### ORCA finished by error termination in SCF gradient [migrated]

I try to optimize and compute frequencies for the system built up from C, O, H, and Co atoms in the following functionals: B2PLYP, B2PLYP-D3, B3LYP, B3LYP-D3, BLYP, BLYP-D3, DSD-PBEP86, PBE, PBE-D3, ... 1 vote
34 views

### How to calculate <ab|ab> integrals to carry out Schwarz pre-screening of molecular integrals

During writing my own two-electron integration library I faced an issue of dealing with integrals that have very small values beyond the C/C++ double data type. ...
25 views

### If you are doing an ONIOM calculation in Gaussian, how do you add both custom MM parameters and a custom basis set using GEN and Amber=SoftFirst?

I am trying to calculate a biological system using AMBER forcefields as my low-layer in ONIOM3. I also want to use a non-native basis set (aug-pc-1 for opt+freq, aug-pc-2 for SPE) that requires custom ...
65 views

### Calculating zero-point energy for the Varshini potential

As per my understanding, for a harmonic oscillator, we can find the zero-point energy by the relation below: $$E_0 = \left(0 + \frac{1}{2}\right)\hbar \omega$$ The equation for the potential in ...
29 views

1 vote
86 views

### Why do DFT calculations output molecular orbitals?

My understanding is that DFT finds the electron density which minimizes some energy functional. How does it make the connection from this optimized density to molecular orbitals?
61 views

### A question regarding hydrogen emission and absorption spectrum

I have read in many articles as well as my textbook that when an electric discharge is passed through a sample of hydrogen gas it excites the electrons and glows emitting light.When this light is ...
69 views

### What is the physical significance of the damping function in calculation of vdW interaction energy?

In order to take care for the singularity (also removing the double counting of exchange-correlation) obtained with this expression, $$E_\mathrm{vdW} = \frac{C^6}{R^6}$$ many type of damping functions ...
197 views

1 vote
53 views

### Computing full Electron-Nuclear Interaction Integrals using Obara-Saika Scheme?

Following my previous question Here, I had been trying to implement One and Two electron integrals in the code. I am currently stuck at the implementation of the OS Scheme, where I read the references ...
220 views

### Can Electron Repulsion Integrals be negative?

I am trying to write a HF code that can calculate the orbital energies for a given molecule at RHF level. I got upto calculating electron repulsion integrals (ERI) and kinetic energy (KE) integrals, ...
1 vote