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
-4
votes
0answers
25 views

Why am I facing an MPI_ABORT problem while running a bulk modulus calculation in quantum espresso? [closed]

Here I am trying to do some testing and I want to do a bulk modulus calculation for an Alloy. I have calculated volume and Energy using BURAI. now when calculating bulk modulus, I face this error ...
1
vote
1answer
41 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 ...
2
votes
0answers
34 views

Reaction pathway - Extra molecule used in one step only?

I am currently building a reaction mechanism through Gaussian calculations. I successfully found each TS and intermediates through the different jobs (opt, freq, irc) for my 3-step mechanism from ...
0
votes
0answers
18 views

How to manually calculate dipole and transition dipole moments from molecular orbital coefficients of DFT calculations?

I have calculated ground and first excited states for some simple molecules ($H_2, H_2O$) with GAUSSIAN software using DFT level of theory and want to manually calculate dipole and transition dipole ...
2
votes
0answers
92 views

Why does having equivalent resonance structures give more stability (Related)?

This question is based on @Heisenberg's Question with the same title. I recently offered a bounty for a more detailed answer for the same question. These are the things I would like to be in the ...
0
votes
1answer
77 views

Classically permitted position values in a quantum harmonic oscillator [closed]

In a quantum harmonic oscillator that is in the state with quantum number $n$, what range of the position $x$ is allowed classically? Does it have something to do with Bohr's correspondence principle?...
1
vote
0answers
25 views

Angle made by orbital with y-axis

What is the hybridization and angle (in degrees) with respect to the y-axis for the following hybrid orbital $ψ=\frac{1}{√3}c×(s-\frac{1}{√3}×p_x+\frac{√3}{√2}×p_y)$ The answer given is 30 degrees but ...
0
votes
1answer
51 views

Schrodinger's Equation and Wave Function

So I understand that there exists the shrodinger's equation, which on solving,gives the wave function of an electron. The wave function as I understand, gives all possible information about an ...
2
votes
0answers
33 views

E1 selection rules for transitions between two Σ states

For E1 selection rules (embodied in the electronic transition moment), to have an allowed transition the direct product of irreducible representations (IRs) must contain the totally symmetric IR. So, ...
5
votes
0answers
89 views

Can cis-trans isomers interconvert?

Can cis-trans isomers interconvert via tunneling ?
2
votes
1answer
28 views

Gaussian calculation - PCM model for IRC compared to gas phase?

Finding a reaction pathway thanks to Gaussian calculations is tricky exercise requiring a lot of resources for each step of this time-consuming process. Thus, man needs to wonder if each calculation ...
1
vote
0answers
21 views

ORCA: meaning of numbers in ORCA.out of MOLECULAR ORBITALS for STO-3G Lithium

For Lithium STO-3G basis set ...
-2
votes
0answers
26 views

How does a bond exist if it is in an electron cloud? [closed]

The electrons that are bonded both have the ability to be wherever they want in the cloud at any time. However, do they both have to be in that spot together as a complete shell, or as individual ...
4
votes
1answer
54 views

How can I get analytical form of GTO primitives for a atom?

As I know, for Hydrogen atom a $1s$ Slater Type Orbital (STO) equation is (I can get it from here): \begin{equation}\label{STO} \mathrm{STO} = \sqrt{\frac{\zeta^3}{\pi}} e^{-\zeta r}. \end{...
4
votes
1answer
143 views

ORCA: How to plot an adiabatic potential in dihydrogen H2 molecule?

I stared to study ORCA, and I try to obtain classical results for dihydrogen as for example. I need to get a starting point to understand what needs to be done. So, How to plot an adiabatic potential ...
1
vote
0answers
28 views

Direction of valence bond and Unsöld's theorem

Is it true that the atomic orbitals of separate atoms already have directionality, which ensures the directionality of the valence bond? Or another words, what is the real spatial distribution of the ...
1
vote
1answer
54 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
28 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 ...
0
votes
2answers
55 views

Why is the radial distribution at the nucleus 0 but not the radial wave function?

The modulus squared of the radial wave function gives the probability of finding an electron in an infinitesimal volume dv. On the other hand, the radial distribution gives the probability of finding ...
1
vote
0answers
35 views

What common observations in chemistry were unexplainable by an early twentieth century chemistry who had no knowledge of relativity

I was reading quite a well-known paper titled 'Relativistic Effects in Structural Chemistry' by PEKKA PYYKKO, and in it, he states that 'it was not until the 1970s that the full relevance of ...
1
vote
1answer
47 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 ...
0
votes
1answer
35 views

Calculating the zero-point energy for the C2N2 molecule

I shall calculate the zero-point energy for the $\ce{C2N2}$ molecule in the $^{1}\Sigma_{g}^{+}$ electron ground state with the following vibrational wavenumbers (symmetries in parentheses) which were ...
2
votes
1answer
74 views

Solution of the Roothaan Equations of H2 by Symmetry Arguments

FWIW my background is in physics and maths, but I am just starting a chemistry PhD (the last time I took a chemistry class was high school). I have only some background in representation theory, and ...
0
votes
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 ...
2
votes
1answer
28 views

Quantum Espresso, phonon band dispersion

I am having a trouble calculating the phonon band dispersion of graphene at $K$-point using Quantum-Espresso, using normconserving+LDA and normconserving+PBE, ecutwfs=60, Ecutrho=400.0, forc_conv_thr=...
0
votes
1answer
56 views

The quantum mechanics behind periodicity of elements

Especially in high school/first-year undergraduate chemistry courses, we learn with great dedication the periodicities along groups and periods. There are various useful and interesting trends. I ...
0
votes
0answers
26 views

Potential energy expectation value and virial theorem

I have been trying to solve this problem Part a) can be proved using the formula . For part b), the expectation value of the potential energy can be calculated from the integral , where Therefore, ...
1
vote
1answer
39 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 ...
14
votes
3answers
521 views

Why do electrons jump back after absorbing energy and moving to a higher energy level?

Electrons in a shell absorb energy and move to higher energy levels, but they release their energy and jump back to the shell they originally were in. Why do they jump back? Why can they not keep ...
0
votes
0answers
28 views

are the exact and kohn-sham electron densities totally symmetric?

For any molecule with open or closed shells considering the electronic state to be the ground state: Is the exact electron density totally symmetric? is the Kohn-Sham electron density totally ...
4
votes
0answers
23 views

How to determine which levels correspond to each other in LS coupling and jj-coupling?

In the LS coupling scheme, L, S and J are good quantum numbers; whereas in jj-coupling scheme, j1,j2 and J are good quantum numbers. I have learnt how to get the term symbols for LS coupling, and for ...
-1
votes
1answer
81 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 ...
1
vote
0answers
78 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 ...
3
votes
1answer
79 views

Heat of reaction for the decomposition of AgCl means?

Certain sunglasses have small crystals of $\ce{AgCl}$ incorporated into the lenses, on exposure to light of appropriate wavelength produces a grey colour to reduce the glare following the reaction: $$\...
5
votes
3answers
335 views

Does electron mass decrease when it changes its orbit?

I have studied this in my chapter atomic structure that when an electron changes its orbit from lower energy to higher energy state , it does not state in my book that it moves there but that it ...
7
votes
1answer
108 views

Is the correct zeroth-order wave function $\phi^{(0)}$ an eigenfunction of the perturbation Hamiltonian $H'$?

Consider the perturbation treatment of He $1s2s$ excited state configuration. The quantum mechanical Hamiltonian for the He-atom is: \begin{aligned} \hat{H} = \sum_{i=1}^2 h_i + \frac 1 {r_{1 2}} \\ ...
2
votes
1answer
40 views

Interpretation of Coloumb operator in Hartree Fock equation

I have read in a textbook (Modern Quantum Chemistry Szabo and Ostlund) that the Coulomb operator of the form \begin{equation} \mathcal{J}_{j}\left(\mathbf{x}_{1}\right)=\int d \mathbf{x}_{2}\left|\...
2
votes
0answers
37 views

Negative coefficients for DIIS in SCF procedure

I am trying to implement the direct inversion of the iterative subspace (DIIS) algorithm in my simple HF program. After some problems it now seems to work. I can calculate the correct energies in ...
0
votes
1answer
78 views

What does Pauli’s exclusion principle mean in atomic or fundamental way? [closed]

It means is that no electron can have same n , l and $m_l$ but can have two different spin quantum number. I want to know why is this rule valid?Means there must be some other things happening also ...
4
votes
1answer
60 views

Which quantum chemistry approximation to use?

I'm just getting started with quantum chemistry using some simple test problems. I have a few of the software packages installed (ASE, Psi4, GPAW etc) and everything is working - no issues with the ...
2
votes
1answer
141 views

Is the quantum number $L$ a combination of the azimuthal and magnetic quantum numbers $(\ell, m_\ell)$?

Somehow, I am getting confused about this... In the $J=L+S$ equation about total angular momentum, which of the four quantum numbers used to describe the electrons and their states is included in the $...
3
votes
1answer
138 views

Is it rigorous enough to change a DFT functional after geometry optimization to calculate excited state properties?

I have done the geometry optimization with the B3LYP functional, however, there is a need to calculate the excited state energy, so the CAM-B3LYP functional should be better suited for that. Do I need ...
0
votes
0answers
34 views

energy difference vs absolute energy

When dealing with determining the ground state energy of a system, people often say that it is better to know the energy difference rather than the absolute minimum energy. I understand that the ...
1
vote
1answer
54 views

Origin of Virtual Molecular Orbitals in Hartree-Fock equations

Let's look at scheme Do I understand correctly, the origin of Virtual Orbitals is a solution of (for, exampre, restricted) HF equation eigenfuncions?
5
votes
0answers
75 views

Stress-Strain Graph Under Uniaxial and Biaxial Strain

I was going through a recently published journal paper by ACS (Applied Nano Materials) about gas separation using nanoporous Graphene. DOI No. - https://dx.doi.org/10.1021/acsanm.0c02340 Supporting ...
0
votes
1answer
59 views

What is the form of the Hamiltonian for solids?

For atoms, and even molecules, I can understand how the Hamiltonian would be constructed, but what of solids (as in, for electronic structure calculations)? Thank you for any help.
0
votes
0answers
16 views

What is the ground-state electron configuration of V2+? [duplicate]

Why do you get rid of the 4s^2 electron subshell first rather than 2 electrons from the 3d subshell?
4
votes
0answers
36 views

What is the definition of energy-independent basis?

I am reading this article by Zatsarinny and Fischer [1]. At some point they span a wave function $\Psi_{E}$ in terms of energy independent basis $$\Psi_{E}=\sum_{k} A_{E k} \Psi_{k}$$ For example, The ...
5
votes
1answer
66 views

Resources to learn second quantization formalism and how to implement it in code for quantum/computational chemistry research

I want to know what are some useful and practical resources to learn the formalism of second quantization as it pertains to fermions to be used in solving Quantum Chemistry problems. I am particularly ...
1
vote
1answer
62 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
2 3 4 5
26