The binding energies of the alginate complexes formed with Ni, Pd, and Pt metal ions of the 4th, 5th, and 6th series were the highest amongst all the metals considered in this work. The computations were carried out in both vapor and aqueous solvent phases and the trends of binding energy were found to be invariant. For computation purposes, one monomer attached from top and bottom to the metal center is considered. The widely accepted egg-box molecular model representation of alginate structures is used for computation purposes. The heavy transition metal ions with + 2 valence in the 4th, 5th, and 6th periods of d-block were considered for the study as most of the heavy metals (e.g., Cu, Cr, Ni, Co, Mn, etc.) are present in this block and significantly contribute to water pollution. To investigate the feasibility of ion exchange of various heavy metal ions, Density Functional Theory (DFT) calculations were carried out using the Gaussian-16 simulation package. These beads are potential adsorbents for the removal of heavy metal ions from water through ion exchange with calcium ions present in the Ca-Alginate matrix. This is generally produced as water-soluble Na alginate which in turn is transformed into water-insoluble Ca-Alginate beads. Performing CI or CASSCF calculations is almost always prohibitive for systems of chemical interest but of course they would be the way to go.Alginate is a naturally occurring linear polysaccharide that is extracted from brown algae. Or just go straight to TDDFT calculations with hybrid orbitals which include a somewhat large percentage of HF exchange and polarized basis sets, but to always compare results to experimental values, if available, since DFT based calculations are Kohn-Sham orbitals which are defined for non-interacting electrons so the energy can be biased. RO calculations could yield wavefunctions with small to large values of spin contamination, so beware. As a consequence, RO calculations and Unrestricted calculations vary due to variational freedom. To the people who have asked me this question I strongly suggest to first try Restricted Open calculations, RODFT, which pair all electrons and treat them with identical orbitals and treat the unpaired ones independently.
by calculating the transitions with such methods like TD-DFT (Time Dependent DFT) and look to the main orbital components of each within the set of α and β densities. Usually the approach is to work backwards when investigating the optical transitions of a, say, organic radical, e.g. Most people will then dismiss the HOMO/LUMO question for open shell systems as meaningless because ultimately we are dealing with two different sets of molecular orbitals. The energy difference between the HOMO and LUMO of any chemical species, known as the HOMO-LUMO gap, is a very useful quantity for describing and understanding the photochemistry and photophysics of organic molecules since most of the electronic transitions in the UV-Vis region are dominated by the electron transfer between these two frontier orbitals.īut when we talk about Frontier Orbitals we’re usually referring to their doubly occupied version in the case of open shell calculations the electron density with α spin is separate from the one with β spin, therefore giving rise to two separate sets of singly occupied orbitals and those in turn have a α-HOMO/LUMO and β-HOMO/LUMO, although SOMO (Singly Occupied Molecular Orbital) is the preferred nomenclature. The central tenet of the FMO theory resides on the idea that most of chemical reactivity is dominated by the interaction between these orbitals in an electron donor-acceptor pair, in which the most readily available electrons of the former arise from the HOMO and will land at the LUMO in the latter. The HOMO – LUMO orbitals are central to the Frontier Molecular Orbital (FMO) Theory devised by Kenichi Fukui back in the fifties.
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