The interesting radical ion pair salts M(2)*(+)TCNQ*(-) (M=Li, Na, K) are a particular class of charge transfer complexes with excess electron. The ground states of these complexes are triplet. The C(2v) symmetry geometrical structures of the M(2)*(+)TCNQ*(-) (M=Li, Na, K) with all-real frequencies are obtained at the density functional theory (DFT) B3LYP/6-31+G(d) level. All calculations of electric properties in this paper have been carried out at the restricted open-shell second order Møller-Plesset perturbation theory (ROMP2) level. Owing to existing excess electron (from the polarized alkali metal atoms) these charge transfer complexes exhibit large nonlinear optical (NLO) responses dominated by excess electron transitions.For these radical ion pair salts M(2)*(+)TCNQ*(-), the static first hyperpolarizabilities (beta(0)) are large. The order of beta(0) values is 19 203 (M=Li)<24 140 (M=Na) < 29 065 a.u. (M=K). Specially, the second hyperpolarizability (gamma(0)) of the complexes with excess electron is obtained for the first time. These static second hyperpolarizabilities are also large. The order of gamma(0) values is 2,213,006 (M=Li)<3,136,754 (M=Na)<7,905,623 a.u. (M = K). Among the three structures, K(2)*(+)TCNQ*(-) has the largest gamma(0) value to be 7.9 x 10(6) a.u. (3982 x 10(-36) esu), which is about 9 times larger than that of the intramolecular charge transfer complex sigma-arylvinylidene trans-[Ru(4-C[double bond, length as m-dash]CHC(6)H(4)C[triple bond, length as m-dash]CC(6)H(4)NO(2))Cl(dppm)(2)]PF(6) [Hurst et al., Organometallics, 2001, 20, 4664]. The present investigation provides a new kind of candidates for the high-performance NLO materials.
We
report the bulk properties and ab initio thermodynamics
surface free energies for α-Fe2O3(0001)
using density functional theory (DFT) with calculated Hubbard U values for chemically distinct surface Fe atoms. There
are strong electron correlation effects in hematite that are not well-described
by standard DFT. A better description can be achieved by using a DFT
+ U approach in which U represents
a Hubbard on-site Coulomb repulsion term. While DFT + U calculations result in improved predictions of the bulk hematite
band gap, surface free energies using DFT + U total
energies result in surface structure predictions that are at odds
with most experimental results. Specifically, DFT + U predictions stabilize a ferryl termination relative to an oxygen
termination that is widely reported under a range of experimental
conditions. We explore whether treating chemically distinct surface
Fe atoms with different U values can lead to improved
bulk and surface predictions. We use a linear response technique to
derive specific U
d values for all Fe atoms
in several slab geometries. We go on to add a Coulomb correction, U
p, to better describe the hybridization between
the Fe d and oxygen p orbitals, accurately predicting the structural
and electronic properties of bulk hematite. Our results show that
the site-specific U
d is a key factor in
obtaining theoretical results for surface stability that are congruent
with the experimental literature results of α-Fe2O3(0001) surface structure. Finally, we use a model surface
reaction to trace how the various DFT + U methods
affect the surface electronic structure and heterogeneous reactivity.
The rapid increase in use of Li-ion batteries in portable electronics has created a pressing need to understand the environmental impact and long-term fate of electonic waste (e-waste) products such as heavy and/or reactive metals. The type of e-waste that we focus on here are the complex metal oxide nanomaterials that compose Li-ion battery cathodes. While in operation the complex metal oxides are in a hermetically sealed container. However, at the end of life, improper disposal can cause structural transformations such as dissolution and metal leaching, resulting in a significant exposure risk to the surrounding environment. The transformations that occur between operational to environmental settings gives rise to a stark knowledge gap between macroscopic design and molecular-level behavior. In this study we use theory and modeling to describe and explain previously published experimental data for cation release from Li(NiMnCo)O (NMC) nanoparticles in an aqueous environment ( Chem. Mater. 2016 (28) 1092-1100). To better understand the transformations that may occur when this material is exposed to the environment, we compute the free energy of surface dissolution, Δ G, from the complex metal oxide NMC for a range of surface terminations and pH.
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