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Questions tagged [wavefunctions]

Refers to a mathematical description of a quantum state of a system.

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8 votes
2 answers
682 views

How do I interpret the Gaussian16 wavefunction file?

I'm new to gaussian16. The wave function file that I obtain as a result of the "Energy" calculation. It consists of five distinct parts : PART 1 : ...
2 votes
1 answer
109 views

Understanding the complexity of geminal-based wavefunctions

Cross-posted on Reddit. I have been reading through [1] to get a better understanding of geminal-based methods. Some short passages are included below: The occupation of each orbital in the expansion ...
3 votes
0 answers
184 views

Understanding derivation of geminal based methods [closed]

Cross-posted on Reddit. I have been reading through [1] to get a better understanding of geminal based methods. This is one of two questions that I'm asking about that paper on this site, the other ...
2 votes
0 answers
126 views

|psi|^2 calculation (1D) for diamond structure silicon not showing full dataset for all bands: Quantum ESPRESSO [closed]

Dear Quantum ESPRESSO users, I was trying to calculate the |psi|^2 calculation (1D) for diamond structure silicon at a single kpoint (gamma point). I have used the semicore pseudopotential that ...
1 vote
0 answers
51 views

Question on known expression (see post) of exact XC functional in analytic (but not closed) form [closed]

This paper analytically solves the "inverse DFT problem" of mapping the ground-state density to the exact XC functional. And the exact density, i.e. the FCC/FCI density, can be expressed as ...
2 votes
3 answers
135 views

Can I freeze f functions from a TZ basis set during MP2 (but not during H-F) to speed up calculations?

This is another question about my molecule; as I'm not doing this as an academical affiliate(I'm currently majoring in mathematics), I have only NWChem and my personal laptop on the mix, and thus need ...
6 votes
0 answers
114 views

Basic but fundamental question on the extended Koopman theorem using Dyson orbitals [closed]

Let there be some ground-state N-electron species named A. A Dyson orbital for Q is defined as the overlap between Q and (Q with one electron removed). The extended Koopmans theorem now states that ...
3 votes
1 answer
29 views

Does the accuracy of RI-MP2 follow the higher number of zetas of the main and fitting bases?

It has been answered to my previous question that RI-MP2/cc-pVTZ/cc-pVTZ gives results of the same quality as MP2/cc-pVTZ. I then started to think about RI-MP2/cc-pVTZ/cc-pVQZ. The term "basis ...
3 votes
1 answer
53 views

Are frozen-core approximations for the elements of first or second row accurate for potentially extremely short bond distances present in the molecule

Yes, it is about my molecule that you've heard of (but never seen) in my previous questions. The molecule, which contains only C, Al, B, Cl, Mg, N, O, S and Si, is macromolecular with quite crowded ...
6 votes
3 answers
498 views

SIESTA output wavefunctions: all vs selected?

Using SIESTA, I want to plot the wavefunctions around the Fermi level (similar to HOMO/LUMO). Also, I want to do COOP analysis. From the SIESTA manual, I can setup to write the wavefunctions ...
4 votes
0 answers
75 views

Do the orbital energies of ground-state Dyson orbitals exactly capture arbitrary excitation energies and/or ionisation potentials/electron affinities? [closed]

According to an answer to my question on whether the Kohn-Sham orbital energies theoretically exactly capture arbitrary ionisation potentials and/or excitation energies, the answer is no for both ...
3 votes
1 answer
190 views

How to get a two-electron expectation value for atoms in PySCF?

I am interested in calculating the following expectation value for atoms using a converged Slater deteminant from in DFT $$ \left< \Psi \left| \sum_{i,j=1}^N r_i^a r_j^b\right| \Psi \right> \; ,\...
11 votes
1 answer
125 views

Wavefunction magnitudes being degenerate everywhere on parameter space even though energy degeneracies occur at isolated points?

Cross-posted here. Consider the usual simple 2-level gapless graphene Hamiltonian in momentum-space where the energy dispersion is degenerate/gapless at a Dirac point: \begin{equation}\tag{1} {\small ...
9 votes
1 answer
103 views

In which theoretical framework does the size of an atom depend on the temperature of the gas (Bose-Einstein condensates)

In order to pose the question, I reproduce an excerpt from this Physics.SE question, about the size of atoms in a Bose-Einstein condensate (BEC): Heisenberg's uncertainty principle in frames of ...
11 votes
1 answer
620 views

What is the minimum basis set one should use?

If I'm interested in getting an answer that is minimally correct what is the minimum basis set level I should use? (i.e. anything less would be much less reliable) Obviously this depends on the ...
5 votes
0 answers
99 views

How to get energy eigenstates using plane wave basis wavefunction .hdf5 output from Quantum ESPRESSO? [closed]

When compiled with the HDF5 flag on, Quantum ESPRESSO (QE) saves wavefunctions in the .save folder. At each k-point, we have an $m\times n$ matrix, where $m$ are the complex number entries of ...
8 votes
0 answers
68 views

Visualizing wavefunctions in real space [closed]

I would like to generate wavefunctions as functions of spatial coordinates (X, Y, Z) using Gaussian G09 and then visualize them. How might I go about doing this? I am using Linux and my preferred ...
5 votes
0 answers
579 views

How can I calculate and plot the molecular orbitals (MO's) from the Gaussian wavefunction file? [closed]

This a follow-up question to my previous question. And as per the answer one could create M.O orbitals from the primitives. As a new user of Gaussian, is there any method (or algorithm) to followed so ...
25 votes
2 answers
399 views

How to overcome the exponential wall encountered in full configurational interaction methods?

Similar to how a molecular orbital, also known as a 1-electron wavefunction, can be represented with a linear combination of “basis” functions, e.g., atomic orbitals (LCAO): $$\Phi(\mathbf{r})=\sum_i^...
11 votes
1 answer
360 views

How to use wavefunctions/density to determine which orbitals lead to edge states?

I have a large matrix for a 1D zigzag edge model of an otherwise $3\times 3$ tight-binding Hamiltonian (3 basis functions, each corresponding to an atomic orbital), involving the variable $k_x$. The ...
12 votes
1 answer
369 views

How to numerically solve real-space 1D time-independent Schrodinger equation using 2D momentum-space Hamiltonian?

Consider the usual simple 2-level graphene Hamiltonian with mass in momentum-space where: $$ H(k,V)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+V\sigma_z], $$ where $t$ is ...
16 votes
1 answer
2k views

Does the Schrödinger equation have unique solutions?

I am learning DFT and the Hohenberg Kohn Theorem of Existence. It says that there is a one-to-one correspondence between the external potential and the density. However the proofs that I have seen ...