Michele Pavanello

Self-Assembled Organic Nanowires for High Power Density Lithium Ion Batteries

The electroactive organic materials are promising alternatives to inorganic electrode materials for the new generation of green Li-ion batteries due to their sustainability, environmental benignity, and low cost. Croconic acid disodium salt (CADS) was used as Li-ion battery electrode, and CADS organic wires with different diameters were fabricated through a facile synthetic route using antisolvent crystallization method to overcome the challenges of low electronic conductivity of CADS and lithiation induced strain. The CADS nanowire exhibits much better electrochemical performance than its crystal bulk material and microwire counterpart. CADS nanowire with a diameter of 150 nm delivers a reversible capability of 177 mAh g(-1) at a current density of 0.2 C and retains capacity of 170 mAh g(-1) after 110 charge/discharge cycles. The nanowire structure also remarkably enhances the kinetics of croconic acid disodium salt. The CADS nanowire retains 50% of the 0.1 C capacity even when the current density increases to 6 C. In contrast, the crystal bulk and microwire material completely lose their capacities when the current density merely increases to 2 C. Such a high rate performance of CADS nanowire is attributed to its short ion diffusion pathway and large surface area, which enable fast ion and electron transport in the electrode. The theoretical calculation suggests that lithiation of CADS experiences an ion exchange process. The sodium ions in CADS will be gradually replaced by lithium ions during the lithiation and delithiation of CADS electrode, which is confirmed by inductively coupled plasma test.

Born-Oppenheimer and non-Born-Oppenheimer, atomic and molecular calculations with explicitly correlated Gaussians.

This paper is part of the 2012 Quantum Chemistry thematic issue. Sergiy Bubin,*,† Michele Pavanello,*,‡ Wei-Cheng Tung, Keeper L. Sharkey, and Ludwik Adamowicz* †Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, United States ‡Department of Chemistry, Rutgers University Newark, Newark, New Jersey 07102, United States Department of Chemistry and Biochemistry and Department of Physics, University of Arizona, Tucson, Arizona 85721, United States

On the subsystem formulation of linear-response time-dependent DFT

A new and thorough derivation of linear-response subsystem time-dependent density functional theory (TD-DFT) is presented and analyzed in detail. Two equivalent derivations are presented and naturally yield self-consistent subsystem TD-DFT equations. One reduces to the subsystem TD-DFT formalism of Neugebauer [J. Chem. Phys. 126, 134116 (2007)]. The other yields Dyson type equations involving three types of subsystem response functions: coupled, uncoupled, and Kohn-Sham. The Dyson type equations for subsystem TD-DFT are derived here for the first time. The response function formalism reveals previously hidden qualities and complications of subsystem TD-DFT compared with the regular TD-DFT of the supersystem. For example, analysis of the pole structure of the subsystem response functions shows that each function contains information about the electronic spectrum of the entire supersystem. In addition, comparison of the subsystem and supersystem response functions shows that, while the correlated response is subsystem additive, the Kohn-Sham response is not. Comparison with the non-subjective partition DFT theory shows that this non-additivity is largely an artifact introduced by the subjective nature of the density partitioning in subsystem DFT.

Very accurate potential energy curve of the LiH molecule.

We present very accurate calculations of the ground-state potential energy curve (PEC) of the LiH molecule performed with all-electron explicitly correlated Gaussian functions with shifted centers. The PEC is generated with the variational method involving simultaneous optimization of all Gaussians with an approach employing the analytical first derivatives of the energy with respect to the Gaussian nonlinear parameters (i.e., the exponents and the coordinates of the shifts). The LiH internuclear distance is varied between 1.8 and 40 bohrs. The absolute accuracy of the generated PEC is estimated as not exceeding 0.3 cm(-1). The adiabatic corrections for the four LiH isotopologues, i.e., (7)LiH, (6)LiH, (7)LiD, and (6)LiD, are also calculated and added to the LiH PEC. The aforementioned PECs are then used to calculate the vibrational energies for these systems. The maximum difference between the computed and the experimental vibrational transitions is smaller than 0.9 cm(-1). The contribution of the adiabatic correction to the dissociation energy of (7)LiH molecule is 10.7 cm(-1). The magnitude of this correction shows its importance in calculating the LiH spectroscopic constants. As the estimated contribution of the nonadiabatic and relativistic effects to the ground state dissociation energy is around 0.3 cm(-1), their inclusion in the LiH PEC calculation seems to be the next most important contribution to evaluate in order to improve the accuracy achieved in this work.

New more accurate calculations of the ground state potential energy surface of H3

Explicitly correlated Gaussian functions with floating centers have been employed to recalculate the ground state potential energy surface (PES) of the H(3) (+) ion with much higher accuracy than it was done before. The nonlinear parameters of the Gaussians (i.e., the exponents and the centers) have been variationally optimized with a procedure employing the analytical gradient of the energy with respect to these parameters. The basis sets for calculating new PES points were guessed from the points already calculated. This allowed us to considerably speed up the calculations and achieve very high accuracy of the results.

Non-Born-Oppenheimer calculations of the pure vibrational spectrum of HeH +

Very accurate calculations of the pure vibrational spectrum of the HeH(+) ion are reported. The method used does not assume the Born-Oppenheimer approximation, and the motion of both the electrons and the nuclei are treated on equal footing. In such an approach the vibrational motion cannot be decoupled from the motion of electrons, and thus the pure vibrational states are calculated as the states of the system with zero total angular momentum. The wave functions of the states are expanded in terms of explicitly correlated Gaussian basis functions multipled by even powers of the internuclear distance. The calculations yielded twelve bound states and corresponding eleven transition energies. Those are compared with the pure vibrational transition energies extracted from the experimental rovibrational spectrum.

Performance of Frozen Density Embedding for Modeling Hole Transfer Reactions.

We have carried out a thorough benchmark of the frozen density-embedding (FDE) method for calculating hole transfer couplings. We have considered 10 exchange-correlation functionals, 3 nonadditive kinetic energy functionals, and 3 basis sets. Overall, we conclude that with a 7% mean relative unsigned error, the PBE and PW91 functionals coupled with the PW91k nonadditive kinetic energy functional and a TZP basis set constitute the most stable and accurate levels of theory for hole transfer coupling calculations. The FDE-ET method is found to be an excellent tool for computing diabatic couplings for hole transfer reactions.

FDE-vdW: A van der Waals inclusive subsystem density-functional theory

We present a formally exact van der Waals inclusive electronic structure theory, called FDE-vdW, based on the Frozen Density Embedding formulation of subsystem Density-Functional Theory. In subsystem DFT, the energy functional is composed of subsystem additive and non-additive terms. We show that an appropriate definition of the long-range correlation energy is given by the value of the non-additive correlation functional. This functional is evaluated using the fluctuation-dissipation theorem aided by a formally exact decomposition of the response functions into subsystem contributions. FDE-vdW is derived in detail and several approximate schemes are proposed, which lead to practical implementations of the method. We show that FDE-vdW is Casimir-Polder consistent, i.e., it reduces to the generalized Casimir-Polder formula for asymptotic inter-subsystems separations. Pilot calculations of binding energies of 13 weakly bound complexes singled out from the S22 set show a dramatic improvement upon semilocal subsystem DFT, provided that an appropriate exchange functional is employed. The convergence of FDE-vdW with basis set size is discussed, as well as its dependence on the choice of associated density functional approximant.

Accurate one-dimensional potential energy curve of the linear (H2)2 cluster.

We present a sub-0.3 K accuracy, ground-state one-dimensional potential energy curve of the metastable linear configuration of the (H(2))(2) cluster calculated exclusively with explicitly correlated Gaussian functions with shifted centers. The H(2) internuclear distance is kept at the isolated H(2) vibrational ground-state average value of 1.448 736 bohr and the intermonomer separation is varied between 2 and 100 bohrs. The analytical gradient of the energy with respect to the nonlinear parameters of the Gaussians (i.e., the exponents and the coordinates of the shifts) has been employed in the variational optimization of the wave function. Procedures for enlarging the basis set and for adjusting the centers of the Gaussians to the varying intermonomer separation have been developed and used in the calculations.

Communication: Visible line intensities of the triatomic hydrogen ion from experiment and theory

The visible spectrum of H3(+) is studied using high-sensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak ro-vibrational transitions from the lowest rotational states of H3(+) up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein B coefficients. Ab initio predictions for the Einstein B coefficients are obtained from a highly precise dipole moment surface of H3(+) and found to be in excellent agreement, even in the region where states have been classified as chaotic.