Periodic and electron density related properties in AtomDB

[gabrielasd]

Properties in AtomDB

This file lists the properties in AtomDB, together with their format. For any of these properties, a "promolecular" value should be possible to define. It will generally be either a mean (perhaps a geometric mean or an l-infinity mean) or a sum of the atomic properties.

Scalars:

Given the atomic number, charge (default to zero), multiplicity (default to ground state of species with that charge and multiplicity), and excitation-level (default to lowest-energy state for a given charge and multiplicity). When fractional charge/multiplicity is provided, the correct thing to do is to define the value from the convex hull. Fractional excitation is not something I know how to support, except perhaps when the fractional occupation is less than one.

• Ionization potential.
• Electron affinity. (same raw data as ionization potentials but accessed differently)
• Electronic Energies (including HF, CI, experiment)
• Atomic radii (as many definitions as possible)
• chemical potentials (benchmark values via the Mulliken-Donnelly-Parr-Levy-Palke definition)
• hardness (benchmark values via the Parr-Pearson definition)
• spin-chemical potential vectors (both native and valence-state-averaged; both {N,S} and {N_alpha,N_beta} representations.)
• spin-hardness matrices (both native and valence-state averaged; both {N,S} and {N_alpha,N_beta} representations.)
• polarizability. I think the best/easiest data is from here, which corresponds to this literature reference. See Thakkar and NIST. Thakkar also has quadrupole polarizabilities. Accurate Noble-Gas data from J. Chem. Phys. 153, 174304 (2020) Thakkar and this last reference include data for selected cations/anions.
• hyperpolarizability; See Thakkar
• softness and spin-softness. (Just utilities to link to the hardness values)

Vectors:

• Orbital energies (HF and/or DFT level). Utility routines for finding the HOMO/LUMO energy should be there, and could be considered "scalar properties" individually.
• Atomic density. (spline of values at specified points.)
• Core atomic density. (spline)
• Valence atomic density (spline)
• kinetic-energy density
• Kohn-Sham potential (wish list; perhaps far off except for certain special cases)
• exchange-correlation energy density (wish list; perhaps far off except for certain special cases)
• fitting coefficients/exponents for Slaters to the density
• fitting coefficients/exponents for MBIS to the density
• fitting coefficients/exponents for Gaussians to the density

It isn't really part of AtomDB per se, but when multiple entries for a data entry are there, we should default to experiment or the highest-accuracy HCI (or similar) calculation we have. That way a user doesn't necessarily have to request a specific piece of data.

Originally posted by @PaulWAyers in https://github.com/QuantumElephant/atomdb/issues/2#issuecomment-812965031

[gabrielasd]

Please follow these links for an idea of the properties being evaluated in each dataset (as they show in master branch)

nist
slater
numeric
gaussian
hci

To the extent that it is possible (given the raw data available) each dataset should cover the properties listed in this issue 1st comment