Softness and polarizability are calculated for different complexions of two-state ensembles of various helium
isoelectronic systems (He, Li+, Be2+, B3+, C4+). It is shown for the first time for the systems studied that an
increase in the excited-state contribution in a two-state ensemble makes the system softer and more polarizable,
as expected from the principles of maximum hardness and minimum polarizability.
Global reactivity parameters like the softness and the polarizability and local reactivity parameters like the
Fukui function and the local hardness have been calculated for the ground (1S) and several excited electronic
states (1P, 1D, 1F) of various helium isoelectronic systems (He, Li+, Be2+, B3+, C4+). Only the lowest energy
state of a given symmetry is chosen because of the validity of the excited state density functional theory
exclusively for this type of states. The softness varies linearly with the cube root of the polarizability for
both the ground and the excited states. It has been demonstrated for the first time for the systems studied
that a system is harder and less
polarizable in its ground state than in any of its excited states. Radial
distributions of the charge density, the Fukui function, and the local hardness exhibit characteristic shell
structures in both the ground and the excited states.
Molecular hardness values have been calculated for a few selected diatomics,viz., H2, HF, N2, BF, CO, and
F2 in their ground and first excited electronic configurations using 4-31G double ζ type basis functions. The
excited electronic configurations are so chosen that they happen to have the lowest energy for a particular
symmetry, keeping in mind the validity of the excited state density functional theory for such systems. It is
observed for all the molecules studied that hardness values decrease with electronic excitation. Surface plots
of different local quantities like the charge density, the laplacian of the charge density, the quantum potential,
the molecular electrostatic potential, and the Fukui function reveal an increase in the molecular reactivity
with excitation.
ABSTRACT:A quantum fluid density functional theory has been developed through an amalgamation of the quantum fluid dynamics and the time-dependent density functional theory. It is used in studying typical time-dependent processes like ion᎐atom collisions and atom᎐field interaction. Temporal evolution of chemical reactivity parameters as electronegativity, hardness, entropy, and polarizability is monitored for a He atom in its ground and excited states interacting with an external electric field and an incoming proton. It is observed that these reactivity parameters either remain static or oscillate with the external field in the atom᎐field interaction case, whereas during the collision process, hardness and entropy maximize and polarizability minimizes for both the electronic states of the atom. The possibility of a quantum theory of motion within the purview of this quantum fluid density functional framework is also explored.
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