Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge density wave and quantum correlation effects arising from edge states. The greater flexibility of a molecular scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topology. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact atomic force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topographical modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.

}, keywords = {boundaries, electronic-properties, magnetic-properties, molybdenum-disulfide, nanoribbons, nanostructures, stability, Surfaces}, issn = {2041-1723}, doi = {10.1038/ncomms12904}, author = {Xu, Hai and Liu, Shuanglong and Ding, Zijing and Tan, Sherman J. R. and Yam, Kah Meng and Bao, Yang and Nai, Chang Tai and Ng, Man-Fai and Lu, Jiong and Zhang, Chun and Loh, Kian Ping} } @article {xi_predicted_2016, title = {Predicted {Unusual} {Catalytic} {Activity} of {One}-{Dimensional} {Pt}-{Induced} {Atomic} {Nanowires} on {Ge}(001) {Surface}}, journal = {Journal of Physical Chemistry C}, volume = {120}, number = {1}, year = {2016}, note = {WOS:000368562200049}, month = {01/2016}, pages = {402{\textendash}406}, abstract = {One dimensional (1D) metal-induced nanowires on a semiconductor surface have attracted enormous interest recently because of their unique electronic properties and great potential in device applications arising from the ideal 1D nature of the systems. Via ab initio modeling, we investigate for the first time the catalytic properties of Pt-induced nanowires (Pt-INWs) on a Ge(001) surface that have been successfully fabricated in experiments. We show that these 1D atomic wires can also be used as excellent catalysts for chemical reaction of CO oxidation. A new ground-state configuration of Pt-INWs on Ge (001) that is significantly more stable than previously reported ones is predicted. The origin of the low reaction barrier of the catalyzed CO oxidation is thoroughly discussed. These results pave the way for a new class of high-performance catalysts with 1D characteristics

}, doi = {10.1021/acs.jpcc.5b10547}, author = {Xi, Yongjie and Guo, Na and Zhang, Chun} } @article {liu_spin-dependent_2016, title = {Spin-dependent electron transport through a {Mn}-phthalocyanine molecule - {A} steady-state density functional theory ({SS}-{DFT}) study}, journal = {Can. J. Chem.}, volume = {94}, number = {12}, year = {2016}, note = {WOS:000390320300004}, month = {12/2016}, pages = {1002{\textendash}1005}, abstract = {We generalize the recently proposed steady-state density functional theory (SS-DFT) to spin-dependent cases and theoretically investigate the electronic and transport properties of a Mn-phthalocyanine molecule sandwiched between two graphene nanoribbon leads. The junction filters spin-up (minority spin) electrons while allowing spin-down (majority spin) electrons to pass with a filtering efficiency of about 99.5\% at low biases. The spin-down electrons are found to tunnel through the junction via the HOMO orbital of the Mn-phthalocyanine molecule. Detailed analysis of the spin-dependent electron tunneling mechanism as well as the electronic/magnetic properties of the junction is presented.

}, keywords = {manganese phthalocyanine, Quantum transport, ss-dft}, issn = {0008-4042}, doi = {10.1139/cjc-2016-0280}, author = {Liu, Shuanglong and Xi, Yongjie and Guo, Na and Yam, Kah Meng and Zhang, Chun} } @article {liu_density_2015, title = {Density {Functional} {Theory} for {Steady}-{State} {Nonequilibrium} {Molecular} {Junctions}}, journal = {Scientific Reports}, volume = {5}, year = {2015}, note = {WOS:000362885600002}, month = {10/2015}, pages = {15386}, abstract = {We present a density functional theory (DFT) for steady-state nonequilibrium quantum systems such as molecular junctions under a finite bias. Based on the steady-state nonequilibrium statistics that maps nonequilibrium to an effective equilibrium, we show that ground-state DFT (GS-DFT) is not applicable in this case and two densities, the total electron density and the density of current-carrying electrons, are needed to uniquely determine the properties of the corresponding nonequilibrium system. A self-consistent mean-field approach based on two densities is then derived. The theory is implemented into SIESTA computational package and applied to study nonequilibrium electronic/transport properties of a realistic carbon-nanotube (CNT)/Benzene junction. Results obtained from our steady-state DFT (SS-DFT) are compared with those of conventional GS-DFT based transport calculations. We show that SS-DFT yields energetically more stable nonequilibrium steady state, predicts significantly lower electric current, and is able to produce correct electronic structures in local equilibrium under a limiting case.

}, doi = {10.1038/srep15386}, author = {Liu, Shuanglong and Nurbawono, Argo and Zhang, Chun} } @article {guo_greatly_2015, title = {Greatly {Enhancing} {Catalytic} {Activity} of {Graphene} by {Doping} the {Underlying} {Metal} {Substrate}}, journal = {Scientific Reports}, volume = {5}, year = {2015}, note = {WOS:000357677600001}, month = {07/2015}, pages = {12058}, abstract = {Graphene-based solid-state catalysis represents a new direction in applications of graphene and has attracted a lot of interests recently. However, the difficulty in fine control and large-scale production of previously proposed graphene catalysts greatly limits their industrial applications. Here we present a novel way to enhance the catalytic activity of graphene, which is highly efficient yet easy to fabricate and control. By first-principles calculations, we show that when the underlying metal substrate is doped with impurities, the catalytic activity of the supported graphene can be drastically enhanced. Graphene supported on a Fe/Ni(111) surface is chosen as a model catalyst, and the chemical reaction of CO oxidation is used to probe the catalytic activity of graphene. When the underlying Fe/Ni(111) substrate is impurity free, the graphene is catalytically inactive. When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed

}, doi = {10.1038/srep12058}, author = {Guo, Na and Xi, Yongjie and Liu, Shuanglong and Zhang, Chun} } @article {nurbawono_modeling_2015, title = {Modeling optical properties of silicon clusters by first principles: {From} a few atoms to large nanocrystals}, journal = {Journal of Chemical Physics}, volume = {142}, number = {15}, year = {2015}, note = {WOS:000353307700045}, month = {04/2015}, pages = {154705}, abstract = {Time dependent density functional tight binding (TDDFTB) method is implemented with sparse matrix techniques and improved parallelization algorithms. The method is employed to calculate the optical properties of various Si nanocrystals (NCs). The calculated light absorption spectra of small Si NCs from TDDFTB were found to be comparable with many body perturbation methods utilizing planewave basis sets. For large Si NCs (more than a thousand atoms) that are beyond the reach of conventional approaches, the TDDFTB method is able to produce reasonable results that are consistent with prior experiments. We also employed the method to study the effects of surface chemistry on the optical properties of large Si NCs. We learned that the optical properties of Si NCs can be manipulated with small molecule passivations such as methyl, hydroxyl, amino, and fluorine. In general, the shifts and profiles in the absorption spectra can be tuned with suitably chosen passivants. (C) 2015 AIP Publishing LLC.

}, doi = {10.1063/1.4918588}, author = {Nurbawono, Argo and Liu, Shuanglong and Zhang, Chun} } @article {nurbawono_odd-even_2015, title = {Odd-{Even} {Effects} in {Charge} {Transport} through {Self}-{Assembled} {Monolayer} of {Alkanethiolates}}, journal = {Journal of Physical Chemistry C}, volume = {119}, number = {10}, year = {2015}, note = {WOS:000351189100047}, month = {03/2015}, pages = {5657{\textendash}5662}, abstract = {It has been demonstrated in experiments that charge transport through self-assembled monolayers (SAMs) of alkanethiolates shows intriguing odd-even effects when the number of methylene groups changes. Most previously reported theoretical investigations were based on semiempirical methods or largely simplified models and the quantum origin of the observed odd-even effects is still unclear. In the current study, we performed ab initio calculations for electronic and transport properties of SAM of alkanethiolates on Ag [111] surface. Extensive density functional theory (DFT) based energy minimizations of the system geometries were conducted to pinpoint the most accurate geometries amenable to experimental observations. The recently proposed dual mean field (DMF) approach that includes bias-induced nonequilibrium effects in density functionals is used to determine current voltage characteristics. Odd-even effects are observed in both electric currents and binding energies between the SAM and the probing electrode. The significant difference between the tunneling barriers across the \"top\" contact of odd and even molecular junctions is revealed to be the origin of the odd-even effects in electron. transport. Our calculations suggest that the odd-even effects in charge transport in the system under study occur for alkanethiolate molecules with a certain length (10 {\textless} n {\textless} 19, where n is the number of methylene groups).

}, doi = {10.1021/jp5116146}, author = {Nurbawono, Argo and Liu, Shuanglong and Nijhuis, Christian A. and Zhang, Chun} } @article {liu_communication:_2013, title = {Communication: Electronic and transport properties of molecular junctions under a finite bias: A dual mean field approach}, journal = {The Journal of Chemical Physics}, volume = {139}, number = {19}, year = {2013}, month = {11/2013}, pages = {191103}, abstract = {We show that when a molecular junction is under an external bias, its properties cannot be uniquely determined by the total electron density in the same manner as the density functional theory for ground state properties. In order to correctly incorporate bias-induced nonequilibrium effects, we present a dual mean field ({DMF)} approach. The key idea is that the total electron density together with the density of current-carrying electrons are sufficient to determine the properties of the system. Two mean fields, one for current-carrying electrons and the other one for equilibrium electrons can then be derived. Calculations for a graphene nanoribbon junction show that compared with the commonly used ab initio transport theory, the {DMF} approach could significantly reduce the electric current at low biases due to the non-equilibrium corrections to the mean field potential in the scattering region.

}, keywords = {Ab initio calculations, Chemical potential, Density functional theory, Electric currents, Electron scattering, Hohenberg Kohn theorem, Mean field theory, Molecular electronic properties, Quantum transport, Transport properties}, issn = {0021-9606, 1089-7690}, doi = {10.1063/1.4833677}, url = {http://scitation.aip.org/content/aip/journal/jcp/139/19/10.1063/1.4833677}, author = {Liu, Shuanglong and Feng, Yuan Ping and Zhang, Chun} } @article {nurbawono_reversible_2013, title = {Reversible magnetism switching in graphene-based systems via the decoration of photochromic molecules}, journal = {Applied Physics Letters}, volume = {103}, number = {20}, year = {2013}, month = {11/2013}, pages = {203110}, abstract = {By first principles calculations, we demonstrate that when decorated with photochromic molecules, it is possible to use light to reversibly control the magnetic properties of a nanoscale magnetic system. The combination of a graphene-based magnetic system and a photochromic azobenzene molecule is chosen as a model system. The trans and cis isomers of the azobenzene molecule that can be converted between each other by means of photoexcitations are found to have drastically different effects on the magnetic properties of the system. The results may pave the way for the future design of light controllable molecular-scale spintronic devices.

}, keywords = {Adsorption, Chemical bonds, Fermi surface, graphene, Magnetic moments, Molecular magnetic properties, Nanomagnetism, Photochromism, Spintronic devices, Vacancies}, issn = {0003-6951, 1077-3118}, doi = {10.1063/1.4831742}, url = {http://scitation.aip.org/content/aip/journal/apl/103/20/10.1063/1.4831742}, author = {Nurbawono, Argo and Zhang, Chun} }