15 votes
Accepted

Does the Schrödinger equation have unique solutions?

The solutions to the Schrödinger equation are not unique in general, and uniqueness depends on several things such as the form of the potential and boundary conditions. Many papers have discussed ...
Nike Dattani's user avatar
  • 33.6k
15 votes
Accepted

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

It is hard to claim that any FCI code overcomes the exponential wall, especially for strongly correlated systems. There are many algorithms, e.g. CDFCI, HCI, FCIQMC, ACI, etc., which significantly ...
Yingzhou Li's user avatar
  • 1,076
14 votes

What is the minimum basis set one should use?

Different people will have slightly different opinions, so take my answer with a grain of salt. I'll try to give the minimum publishable basis sets, i.e. if you use worse basis sets than these, you'll ...
wzkchem5's user avatar
  • 9,076
10 votes
Accepted

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

One way of determining this is using the projected density of states (P-DOS) This resolves the DOS into specific orbitals thereby allowing you to discretize each orbitals weight for a specific energy. ...
nickpapior's user avatar
  • 3,084
9 votes
Accepted

How do I interpret the Gaussian16 wavefunction file?

I have yet to find a source that lays this out explicitly, but from the examples I could find, it is not too hard to infer the meaning of these sections. To start with (and possibly point you in the ...
Tyberius's user avatar
  • 15.2k
8 votes

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

Not all determinants contribute significant correlation, especially configurations for excitations of multiple electrons to higher energy orbitals, which is the basis for CAS methods; i.e. only choose ...
Alan Rask's user avatar
6 votes
Accepted

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

As you mention, your graphene hamiltonian operates on sites, i.e. it is a lattice model. Its solution therefore does not provide a wave function in real space, it provides wave function amplitudes on ...
leopold.talirz's user avatar
5 votes
Accepted

SIESTA output wavefunctions: all vs selected?

The two different files contain different things: *.fullBZ.WFSX contains all wavefunctions for the SCF sampled Brillouin zone, i.e. for all k-points defined in the ...
nickpapior's user avatar
  • 3,084
5 votes

SIESTA output wavefunctions: all vs selected?

I believe both can technically be used. Let me first point out that your calculation must have been long and heavy ! Good luck with those. Your fullBZ.WFSX files are used for the COOP bonding analysis ...
Elie H's user avatar
  • 1,402
4 votes

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

This is a somewhat handwaving answer but I think it gets the main point across: We should start by pointing out that the two components of your eigenstates represent the wave function amplitudes on ...
leopold.talirz's user avatar
4 votes

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

In calculations of the electronic energy/wavefunction, temperature typically is not taken in to account (besides cases of orbital occupation smearing, though this is used more as a computational trick ...
Tyberius's user avatar
  • 15.2k
3 votes

SIESTA output wavefunctions: all vs selected?

An alternative way to explore the states around a given energy is to compute the "local density of states", which is a kind of "charge density" obtained from the states in a given ...
albertog's user avatar
3 votes

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

The term "basis set" literally comes from Fourier analysis in mathematics, and in Fourier analysis the "errors" systematically "cancel out", for example when integrating ...
Susi Lehtola's user avatar
2 votes

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

The answer is no. Post-Hartree-Fock methods are famously slow to converge to the complete basis set limit due to their dependence on the unoccupied orbitals. Modern basis sets, such as the Dunning cc-...
Susi Lehtola's user avatar
2 votes
Accepted

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

It depends on what you're intending to do: If you are comparing to benchmark results with this basis set, then likely no. If accuracy is very important to you, then likely no. If you are intending to ...
Nike Dattani's user avatar
  • 33.6k
2 votes
Accepted

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

Due to the errors associated with your choice of functional (even if it's a double hybrid functional), I think there is not much value in unfreezing the core with regards to getting more accurate ...
Nike Dattani's user avatar
  • 33.6k
2 votes

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

First of all, the "diagonal" contribution of Eq. (1), $$ \langle \Psi | \sum_i^N r_i^{a+b} | \Psi \rangle \tag{3} $$ is the expectation value of a one-body operator, so you already know how ...
wzkchem5's user avatar
  • 9,076
2 votes
Accepted

Understanding the complexity of geminal-based wavefunctions

"Why does the paragraph after expression (10) says that AGP has a complexity of O(K^2) which contradicts its own sentences just after expression (5) about having binomial complexity? Expression ...
Nike Dattani's user avatar
  • 33.6k
1 vote

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

I'm not sure if freezing at the basis set level makes sense... However, you can make an MP2 calculation easier, by doing an active space approximation (freezing certain orbitals). You will need to ...
lex2763's user avatar
  • 321
1 vote

How do I interpret the Gaussian16 wavefunction file?

https://aim.tkgristmill.com/wfxformat.html WFX format specification. WFX is an AIM file. Yes, Cartesian. https://wordpress.nmsu.edu/tmanz/files/2020/06/WFX_file_programmers_guide_06_14_2020.pdf WFX ...
Steve C's user avatar
  • 11

Only top scored, non community-wiki answers of a minimum length are eligible