Quantum Fluid Density Functional Theory Research Articles

Conceptual DFT based electronic structure principles in a dynamical context

Within the context of quantum fluid density functional theory diverse processes simulating a chemical reaction like interaction of an atom or a molecule with an externally applied electric or magnetic field or its collision with a proton have been analyzed in a dynamical situation. The changes produced in the chemical reactivity parameters namely chemical potential, hardness, polarizability during such processes have been identified and discussed. In addition, confinement is also introduced to observe the necessary variation in the different reactivity parameters.

Reactivity Dynamics.

The chemical reactivity of a molecule as a whole or of an atom in a molecule varies during a chemical reaction. A variation of global and local reactivity descriptors in the course of a physicochemical process was studied within a quantum fluid density functional theory framework. Effects of a physical confinement and the electronic excitation therein were studied. In this Perspective, we also highlight the direction of a spontaneous chemical reaction in the light of the dynamical variants of the conceptual density functional theory-based electronic structure principles. An exhaustive state-of-the-art dynamical study is warranted in order to understand a chemical reaction from a reactivity perspective augmenting the associated molecular reaction dynamics analysis.

Dynamical deformations of the electron density in an H2 molecule under strong, oscillating magnetic fields: an application of time-dependent quantum fluid density functional theory

ABSTRACTFollowing the time-dependent quantum fluid density functional theory developed in our laboratory, the present quantum-mechanical, dynamical study of the H2 molecule under strong, oscillating magnetic fields reveals a coexistence of both slow and fast dynamics, as seen earlier in the cases of hydrogen and helium atoms. Using the Deb–Chattaraj equation of motion we find that, contrary to the situation with static magnetic fields, the electron density now transiently expands. Consequently, the fate of the H–H bond under such strong TD magnetic fields has been addressed through detailed and accurate TD density profiles computed by direct numerical solution of the real-time evolution equation. A detailed interpretation of the slow dynamics has been made.

Reactivity dynamics of a confined molecule in presence of an external magnetic field

Reactivity dynamics and stability of a confined hydrogen molecule in presence of an external magnetic field has been studied using quantum fluid density functional theory. Dynamic profiles of various reactivity parameters such as hardness, electrophilicity, magnetizability, phase volume, entropy, etc. have been studied within a confined environment. Responses in the reactivity parameters as well as the associated electronic structure principles validate the stability of the confined H2 molecule in ground and excited states in presence of an external magnetic field. Confinement to the system has been imposed by the Dirichlet type boundary condition. Confinement and excitation act in opposite directions. Ground state type dynamics is obtained on simultaneous electronic excitation and confinement. © 2014 Wiley Periodicals, Inc.

Density dynamics in some quantum systems

The quantum domain behavior of classical nonintegrable systems is well-understood by the implementation of quantum fluid dynamics and quantum theory of motion. These approaches properly explain the quantum analogs of the classical Kolmogorov–Arnold–Moser type transitions from regular to chaotic domain in different anharmonic oscillators. Field-induced tunneling and chaotic ionization in Rydberg atoms are also analyzed with the help of these theories. Quantum fluid density functional theory may be used to understand different time-dependent processes like ion-atom/molecule collisions, atom-field interactions, and so forth. Regioselectivity as well as confined atomic/molecular systems and their reactivity dynamics have also been explained. © 2013 Wiley Periodicals, Inc.

Molecular reactivity dynamics in a confined environment

Time evolution of various reactivity parameters viz. hardness, electrophilicity, chemical potential, polarizability, etc. in a confined environment has been studied through quantum fluid density functional theory formalism during time dependent processes such as proton-molecule collisions and molecule-field interaction. A Dirichlet type boundary condition has been incorporated to confine the systems. Responses in the reactivity parameters of the diatomic molecules, in the dynamical context, in ground state as well as in excited state, have been reported. Harmonic spectra are generated in the cases of the external laser field interacting with H2 and N2 molecules.

A tug-of-war between electronic excitation and confinement in a dynamical context

Quantum fluid density functional theory has been used to study the time evolution of various reactivity parameters such as hardness, electrophilicity, entropy, chemical potential, polarizability, electronegativity etc. in a confined environment during time dependent processes like atom-ion collision and atom-field interaction. Responses in the reactivity parameters of the helium atom, in the dynamical context, for ground state as well as in excited state, have been reported. The confinement is incorporated through a Dirichlet type boundary condition. With a decrease in the size of the cylindrical box, the system gets harder and less polarizable. Simultaneous excitation and confinement may bring back the ground state behavior.

Quantum fluid density functional theory of chemical reactivity in a two-state ensemble

A quantum fluid density functional approach is adopted in monitoring the dynamics of various global and local reactivity parameters of a helium atom in a two-state equiensemble, having an interaction with an external laser field as well as an incoming proton. The effect of an increase in the excited-state contribution in a two-state ensemble is more pronounced in global reactivity parameters than the local ones. Global reactivity indices are found to be more sensitive to the external perturbation, for the whole time-dependent process, than the local indices. Most of the local quantities show drastic changes only at the beginning of the processes. In the atom–field interaction problem, electronegativity, polarizability and entropy oscillate with the field and hardness attains a steady value after the initial transients die out. The ion–atom collision process can be divided into three distinct regimes in terms of the time-dependent electronegativity profile. In the encounter regime, hardness and entropy maximize and polarizability minimizes. Dynamical variants of the principles of maximum hardness, maximum entropy and minimum polarizability are shown to be operative.

Quantum fluid density functional theory of time‐dependent processes

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. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 279–291, 1998

Quantum fluid density functional theory of time-dependent processes

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. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 279–291, 1998

Electronegativity and hardness profiles of a chemical process: Comparison between quantum fluid density functional theory andab initio SCF method

Temporal evolution of electronegativity and hardness associated with a collision process between a Be atom and a proton has been studied within a quantum fluid density functional framework. In the presence of a third collisional partner to take away excess energy, this collision may lead to a chemical reaction producing a BeH+ molecule. For comparisonab initio SCF level calculation (with 6–31G** basis set) on BeH+ molecule with different geometries have been performed. Electronegativity equalization and maximum hardness principles are analyzed.

Quantum fluid density functional theory of helium atom in an intense laser field

AbstractDynamic response of a helium atom in an intense laser field has been studied within a quantum fluid density functional framework. Several time‐dependent quantities have been calculated by solving a recently derived generalized nonlinear Schrödinger equation.

Time-dependent quantum-fluid density-functional study of high-energy proton-helium collisions.

A quantum-fluid density-functional theory (QF DFT) is proposed, yielding a time-dependent (TD) generalized nonlinear Schr\"odinger equation (GNLSE) as the equation of motion (EOM) for dealing with proton--helium-atom collisions from ``start'' to ``finish.'' The EOM contains the Weizs\"acker term as the kinetic-energy functional, apart from local exchange and correlation functionals. The GNLSE is numerically solved in cylindrical polar coordinates by a leapfrog-type finite-difference algorithm. Various TD quantities such as difference density (DD), induced-dipole moment (IDM), dipole polarizability tensor component, reaction probability, etc., have been studied to obtain physical insights into the mechanism of the TD collision process. In particular, the DD and the oscillating IDM permit a natural partitioning of the p-He collision process into approach, encounter, and departure regimes. The TD DD profiles reveal that, as a result of the interaction, p\ensuremath{\sigma} densities mix substantially into the 1s density of the He atom. Critical comments are made on the usefulness of the QF DFT approach for understanding TD processes.