EMSL: Jun Li's Publications

De Silva MH, J Li, Z Zheng, and LR Corrales. 2008. "Correlation of Calculated Excited-state Energies and Experimental Quantum Yields of Luminescent Tb(III) β-diketonates." Journal of Physical Chemistry A 112(20):4527-4530. doi:10.1021/jp8002799 Abstract Theoretical calculations employing time dependent density functional theory (TDDFT) are used to characterize the excited states of Tb(III) β-diketonate complexes. Calculated results are compared directly with experimental results that together show a correlation between relative quantum yields and the excited-state energies that depend on the electronic properties of the p,p’- substituent group associated with the coordinating N-donor neutral ligand. It is found that changes in the electron donating nature of the neutral ligand structure leads to shifts in the lowest triplet energy level of the complex that consequently changes the relative quantum yield. Thus providing critical direction for the synthesis of high quantum yield terbium complexes.

Pan LL, J Li, and LS Wang. 2008. "Low-Lying Isomers of the B9- Boron Cluster: The Planar Molecular Wheel Versus Three-Dimensional Structures." Journal of Chemical Physics 129(2):187-193. Article number: 024302. doi:10.1063/1.2948405 Abstract The B9- cluster was found previously to be an unprecedented molecular wheel containing an octacoordinate planar boron with D8h symmetry in a combined photoelectron spectroscopy (PES) and theoretical study [H. J. Zhai et al., Angew. Chem. Int. Ed. 42, 6004 (2003)]. However, the PES spectra of B9- exhibit minor features that cannot be explained by the global minimum D8h structure, suggesting possible contributions from low-lying isomers at finite temperatures. Here we present Car-Parrinello molecular dynamics with simulated annealing simulations to fully explore the potential energy surface of B9- and search for low-lying isomers that may account for the minor PES features. We performed density functional theory (DFT) calculations with different exchange-correlation functionals and ab initio calculations at various levels of theory with different basis sets. Two three-dimensional low-lying isomers were found, both of Cs symmetry, 6.29 (Cs-2) and 10.23 (Cs-1) kcal/mol higher in energy than the D8h structure at the highest CCSD(T) level of theory. Calculated detachment transitions from the Cs-2 isomer are in excellent agreement with the minor features observed in the PES spectra of B9-. The B9- cluster proves to be a challenge for most DFT methods and the calculated relative energies strongly depend on the exchange-correlation functionals, providing an excellent example for evaluating the accuracies of various DFT methods.

Zhai HJ, LL Pan, B Dai, B Kiran, J Li, and LS Wang. 2008. "Chemisorption-Induced Structural Changes and Transition from Chemisorption to Physisorption in Au6(CO)n-(n=4-9)." Journal of Physical Chemistry C 112(31):11920-11928. doi:10.1021/jp803161b Abstract The interactions of CO with gold clusters are essential to understanding the catalytic mechanisms of CO oxidation on supported gold nanoparticles. Here we report a photoelectron spectroscopy and theoretical study of CO adsorption on a well-defined Au6− cluster in Au6(CO)n− (n = 4-9). Previous studies have shown that the first three CO successively bind the three apex sites of the triangular Au6−. The current work reveals that the forth CO induces a major structural change to create more apex sites to accommodate the additional CO. Definitive spectroscopic evidence is obtained for the chemisorption saturation at Au6(CO)6 −, in which Au6 has rearranged to accommodate the six CO adsorbates. The photoelectron spectra of larger clusters from Au6(CO)7 − to Au6(CO)9 − are observed to be almost identical to that of Au6(CO)6 −, suggesting that the additional CO’s are simply physisorbed onto the Au6(CO)6 − core. Quasirelativistic density functional calculations are performed on both Au6(CO)n and Au6(CO)n − (n = 4-6). The theoretical results are used to interpret the experimental observations and provide insight into the nature of CO interactions with gold clusters. The Au6 cluster is shown to be highly fluxional upon multiple CO adsorptions, stabilizing structures with more apex sites to accommodate the additional CO’s. The CO-induced structural transformation is analogous to structural flexibility and mobility in heterogeneous catalysis. The observations of the propensity of CO toward apex sites and CO-induced structural changes in small gold clusters m

Cui L, X Huang, L Wang, J Li, and LS Wang. 2007. "Endohedral Stannaspherenes M@Sn12-: A Rich Class of Stable Molecular Cage Clusters." Angewandte Chemie International Edition 46(5):742-745. doi:10.1002/anie.200603226 Abstract Experimental and theoretical evidence is reported that the icosahedral stannaspherene Sn12 2- cage can trap an atom from any of the transition-metal series or the f-elements, giving rise to a myriad of stable endohedral clusters. A selected set of M@Sn12 - cluster has been created using laser vaporization and characterized by photoelectron spectroscopy. It is shown that these clusters maintain perfect or pseudo-icosahedral symmetry with the central metal atom inducing very little distortion to the stannaspherene cage. The doped atom in M@Sn12 - keeps its quasiatomic nature with large magnetic moments. The endohedral stannaspherenes might thus be viewed as “superatoms”, yielding potentially a rich class of new building blocks for clusterassembled materials with tunable magnetic, electronic, and chemical properties.

Gu X, S Bulusu, X Li, XC Zeng, J Li, XG Gong, and LS Wang. 2007. "Au34-: A Fluxional Core-Shell Cluster." Journal of Physical Chemistry C 111(23):8228-8232. doi:10.1021/jp071960b Abstract Among the large Aun – clusters for n > 20, the photoelectron spectra of Au34 – exhibit the largest energy gap (0.94 eV) with well-resolved spectral features, making it a good candidate for structural consideration in conjunction with theoretical studies. Extensive structural searches at several levels of theory revealed that the low-lying isomers of Au34 – can be characterized as fluxional core-shell type structures with 4 or 3 inner atoms and 30 or 31 outer atoms, i.e., Au4@Au30 – and Au3@Au31 –, respectively. Detailed comparisons between theoretical and photoelectron results suggest that the most probable ground state structures of Au34 – are of the Au4@Au30 – type. The 30 outer atoms seem to be disordered or fluxional, giving rise to a number of low-lying isomers with very close energies and simulated photoelectron spectra. The fluxional nature of the outer layer in large gold clusters or nanoparticles may have important implications for their remarkable catalytic activities.

Li J, SM Kathmann, GK Schenter, and MS Gutowski. 2007. "Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials." Journal of Physical Chemistry C 111(8):3294-3299. doi:10.1021/jp066360b Abstract Boron-nitrogen-hydrogen (BNHx) materials are polar analogs of hydrocarbons with potential applications as media for hydrogen storage. As H(NH₂BH₂)nH oligomers result from dehydrogenation of NH₃BH₃ and NH₄BH₄ materials, understanding the geometries, stabilities, and electronic structure of these oligomers is essential for developing chemical methods of hydrogen release and regeneration of the BNHx-based hydrogen storage materials. In this work we have performed computational modeling on the H(NH₂BH₂)nH (n = 1 – 6) oligomers using density functional theory (DFT). We have investigated linear chain structures and the stabilizing effects of coiling, biradicalization, and branching through Car-Parrinello molecular dynamics simulations and geometry optimizations. We find that the zig-zag linear oligomers are unstable with respect to the coiled, square-wave chain, and branched structures, with the coiled structures being the most stable. Dihydrogen bonding in oligomers, where protic Hδ⁺(N) hydrogens interact with hydridic Hδ⁻(B) hydrogens, plays a crucial role in stabilizing different isomers and conformers. The results are consistent with structures of products that are seen in experimental NMR studies of dehydrogenated ammonia borane.

Schuchardt KL, BT Didier, TO Elsethagen, L Sun, V Gurumoorthi, JM Chase, J Li, and TL Windus. 2007. " Basis Set Exchange: A Community Database for Computational Sciences ." Journal of Chemical Information and Modeling 47(3):1045-1052. doi:10.1021/ci600510j Abstract Basis sets are one of the most important input data for computational models in the chemistry, materials, biology and other science domains that utilize computational quantum mechanics methods. Providing a shared, web accessible environment where researchers can not only download basis sets in their required format, but browse the data, contribute new basis sets, and ultimately curate and manage the data as a community will facilitate growth of this resource and encourage sharing both data and knowledge. We describe the Basis Set Exchange (BSE), a web portal that provides advanced browsing and download capabilities, facilities for contributing basis set data, and an environment that incorporates tools to foster development and interaction of communities. The BSE leverages and enables continued development of the basis set library originally assembled at the Environmental Molecular Sciences Laboratory.

Zubarev DY, AI Boldyrev, J Li, H Zhai, and LS Wang. 2007. "On The Chemical Bonding of Gold In Auro-Boron Oxide Clusters AunBO-(n=1-3)." Journal of Physical Chemistry A 111(9):1648-1658. doi:10.1021/jp0657437 Abstract During experiment on Au-B alloy clusters, an auro-boron oxide cluster Au2BO- was observed to be an intense peak dominating the Au-B mass spectra, along with weaker signals for AuBO- and Au3BO-. Well-resolved photoelectron spectra have been obtained for the three new oxide clusters, which exhibit an odd-even effect in their electron binding energies. Au2BO- is shown to be a closed shell molecule with a very high electron binding energy, whereas AuBO and Au3BO neutrals are shown to be closed shell species with large HOMO-LUMO gaps, resulting in relatively low electron affinities. Density functional calculations were performed for both AunBO- (n = 1-3) and the corresponding HnBO- species in order to evaluate the analogy in bonding between gold and hydrogen in B-Au clusters. The combination of experiment and theory allowed us to establish the structures and chemical bonding of these tertiary clusters. We find that the first gold atom does mimic hydrogen and interacts with the BO unit to produce a linear AuBO- structure. This unit preserves its identity when interacting with additional gold atoms: a linear Au-[AuBO] complex is formed when adding one extra Au atom and two isomeric Au2-[AuBO] complexes are formed when adding two extra Au atoms. Since BO- is isoelectronic to CO, the AunBO- species can be alternatively viewed as Aun interacting with a BO- unit. The structures and chemical bonding in AunBO- are compared to those in the corresponding AunCO complexes.

Cui L, X Huang, L Wang, J Li, and LS Wang. 2006. "Pb-12(2-): Plumbaspherene." Journal of Physical Chemistry A 110(34):10169-10172. Abstract Photoelectron spectroscopy and theoretical calculations show that Pb122- is a highly stable icosahedral cage cluster, similar to Sn122-. It is bonded by four delocalized radial bonds and nine delocalized on-sphere bonds from the 6p orbitals of the Pb atoms. Following Sn122- (stannaspherene), we coin a name, plumbaspherene, for the highly stable and nearly spherical Pb122- cluster, which has a diameter of ~6.3 Å with an empty interior volume large enough to host most transition metal atoms and afford a new class of stable endohedral plumbaspherenes similar to the endohedral fullerenes.

Cui L, X Huang, L Wang, DY Zubarev, AI Boldyrev, J Li, and LS Wang. 2006. "Sn₁₂²⁻: Stannaspherene." Journal of the American Chemical Society 128(26):8390-8391. doi:10.1021/ja062052f Abstract The Sn₁₂²⁻ cluster is discovered to be a highly stable and highly symmetric icosahedral cage bonded by four delocalized radial π bonds and nine delocalized onsphere bonds from the 5p orbitals of the Sn atoms. It has a diameter of 6.1 Å with a large empty interior volume and can host most transition metal atoms inside, giving rise to a large class of endohedral chemical building blocks for cluster-assembled nanomaterials.