Is direct wavefunction analysis meaningful?

[hongyi-zhao]

Hi,

I noticed the pyzfs package is based on wavefunction analysis, hence I post my following question relevant to wavefunction analysis. See following for more info.

See the notes from here, as shown below:

The wave function has no direct physical meaning.  It is just one way
of storing information.  It stores all the information available to
the observer about the system.  To make predictions about the outcome
of all measurements, at any time, one has to "do" something to the
wave function to extract information.  One has to perform some
mathematical operation on it, such a squaring it, multiplying it by a
constant, differentiating it, etc.  One has to operate on the wave
function with some operator.  (The operator is a specific instruction
or set of instructions.)  Every observable is associated with its own
operator.

I want to know whether it really makes sense to analyze the real or imaginary parts of a wavefunction directly.

Regards, HY

[hema-ted]

PyZFS evaluates the expectation value of dipole-dipole interaction on the Slater determinant of Kohn-Sham orbitals. I don't think PyZFS performs the kind of "wavefunction analysis" that you mentioned.

With that being said, Kohn-Sham orbitals and eigenvalues does not have direct physical meaning. However, for many important questions in chemistry and materials science, one cannot afford performing ab initio wavefunction theory calculations, thus in many cases people use KS orbitals and eigenvalues to derive physical quantities of the system, although this is an approximation.

[hongyi-zhao]

PyZFS evaluates the expectation value of dipole-dipole interaction on the Slater determinant of Kohn-Sham orbitals.

Any more explanations on the dipole-dipole interaction on the Slater determinant of Kohn-Sham orbitals?

I don't think PyZFS performs the kind of "wavefunction analysis" that you mentioned.

With that being said, Kohn-Sham orbitals and eigenvalues does not have direct physical meaning. However, for many important questions in chemistry and materials science, one cannot afford performing ab initio wavefunction theory calculations,

Confusing descriptions. Based on my current understanding, PyZFS package is interfaced with some first-principles codes, which in turn do the corresponding ab initio wavefunction theory calculations. Why you still say one cannot afford performing ab initio wavefunction theory calculations?

Do you mean the analytical solution to Schrödinger equation?

thus in many cases people use KS orbitals and eigenvalues to derive physical quantities of the system, although this is an approximation.

This is just the thing done by most of the ab initio codes, IMO.

[hema-ted]

DFT vs wavefunction theory for ZFS calculation: see e.g. 10.1021/jp0643303. The equation used in PyZFS for evaluating ZFS on KS orbitals as expectation values: 10.21105/joss.02160 second equation.

[hongyi-zhao]

DFT vs wavefunction theory for ZFS calculation: see e.g. 10.1021/jp0643303.

The title of this paper is: Spin−Spin Contributions to the Zero-Field Splitting Tensor in Organic Triplets, Carbenes and Biradicals - A Density Functional and Ab Initio Study.

But what's the differences between the terminologies Density Functional and Ab Initio? In my impression, many times they are equivalent/confused.