  Due to its efficiency and reasonable accuracy, density functional theory is
one of the most widely used electronic structure theories in condensed matter
physics, materials physics, and quantum chemistry. The accuracy and efficiency
of a density functional is dependent on the basic ingredients it uses, and how
the ingredients are built into the functional as a whole. An iso-orbital
indicator based on the electron density, its gradients, and the kinetic energy
density, has proven an essential dimensionless variable that allows density
functionals to recognise and correctly treat various types of chemical bonding,
both strong and weak. Density functionals constructed around the iso-orbital
indicator usually require dense real-space grids for numerical implementation
that deteriorate computational efficiency, with poor grid convergence
compromising the improved accuracy. Here, a novel iso-orbital indicator is
proposed based on the same ingredients that retains the capability to identify
the same chemical bonds while significantly relieving the requirement of dense
grids, and giving an improved recognition for tail regions of electron
densities. The novel iso-orbital indicator is therefore expected to be the
prime choice for further density functional development.
