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Ab Initio

Iker León, Fernando Ruipérez, Jesus M Ugalde, Lai-Sheng Wang
We report an investigation of a series of auropolyynes, Au-(C≡C) n -Au- ( n = 1-3), using high-resolution photoelectron imaging and ab initio calculations. Vibrationally resolved photoelectron spectra are obtained, allowing the electron affinities of Au-(C≡C) n -Au to be accurately measured as 1.651(1), 1.715(1), and 1.873(1) eV for n = 1-3, respectively. Both the Au-C symmetric stretching and a bending vibrational frequency are observed for each neutral auropolyyne. Theoretical calculations find that the ground state of Au2 C2 - has a linear acetylenic Au-C≡C-Au- structure, whereas the asymmetric Au-Au-C≡C- structure is a low-lying isomer...
October 14, 2018: Journal of Chemical Physics
Christof Holzer, Xin Gui, Michael E Harding, Georg Kresse, Trygve Helgaker, Wim Klopper
A variety of approaches are presented for the computation of atomic and molecular correlation energies based on the Bethe-Salpeter equation in the framework of the adiabatic-connection fluctuation-dissipation theorem. The performance of the approaches is assessed by computing the total energies of the atoms H-Ne and the atomization energies of the high-accuracy extrapolated ab initio thermochemistry set of small molecules as well as by determining the bond lengths and harmonic vibrational frequencies of the metal monoxides MO with M=Ca-Zn...
October 14, 2018: Journal of Chemical Physics
Simon P Neville, Albert Stolow, Michael S Schuurman
Cyclopropane, the smallest organic ring compound, exhibits complex spectroscopy and excited state dynamics. In Paper I, we reinterpret the vacuum ultraviolet (VUV) electronic absorption spectrum of cyclopropane via ab initio computation. The first two bands in the VUV spectrum are simulated using wavepacket propagations employing the multiconfigurational time-dependent Hartee method and a newly parameterized linear vibronic coupling Hamiltonian. The parameters of the model Hamiltonian are obtained directly from high level multireference configuration interaction calculations...
October 14, 2018: Journal of Chemical Physics
Guo-Jin Cao
Recently, the T-Hg(ii)2 -A base pair containing two equivalents of Hg(ii) has been prepared and characterized experimentally, which implies that there might exist considerable stable metal-mediated base pairs holding two neighbouring metal centers. Here we report a quantum chemical study on geometries, electronic structures, and bonding of various G2 Cu2 4+ (G = guanine) isomers including one di-copper(i) unit. Different density functional methods [Becke 3-parameter-Lee-Yang-Parr, Perdew-Becke-Ernzerhof, Becke-Perdew, Density Functional Theory with Dispersion Corrections (DFT-D)] assign ambiguous relative energies to these isomers with the singlet and triplet states...
October 14, 2018: Journal of Chemical Physics
Sagarmoy Mandal, Jayashrita Debnath, Bernd Meyer, Nisanth N Nair
Plane wave basis sets offer many advantages in ab initio molecular dynamics due to their efficiency and simplicity. In combination with hybrid density functionals, they become computationally expensive due to the evaluation of the Hartree-Fock exchange energy. The computational cost can be significantly reduced by screening the Kohn-Sham orbital products after localizing the orbitals in real space. However, such a procedure introduces apparent errors in the wavefunctions and nuclear forces resulting in unstable dynamics...
October 14, 2018: Journal of Chemical Physics
Michael R Coates, Martin A B Larsen, Ruaridh Forbes, Simon P Neville, Andrey E Boguslavskiy, Iain Wilkinson, Theis I Sølling, Rune Lausten, Albert Stolow, Michael S Schuurman
The vacuum-ultraviolet photoinduced dynamics of cyclopropane (C3 H6 ) were studied using time-resolved photoelectron spectroscopy (TRPES) in conjunction with ab initio quantum dynamics simulations. Following excitation at 160.8 nm, and subsequent probing via photoionization at 266.45 nm, the initially prepared wave packet is found to exhibit a fast decay (<100 fs) that is attributed to the rapid dissociation of C3 H6 to ethylene (C2 H4 ) and methylene (CH2 ). The photodissociation process proceeds via concerted ring opening and C-C bond cleavage in the excited state...
October 14, 2018: Journal of Chemical Physics
W Orellana, Susanna L Stephens, Wallace C Pringle, Peter Groner, Stewart E Novick, S A Cooke
Vinylsulfur pentafluoride (VSPF), a molecule with a four-fold internal rotor, -SF4 , has been studied with high resolution Fourier transform microwave spectroscopy. We believe that this is the first report of resolved four-fold internal rotation. As such, we have presented the tools needed to understand and analyze such a problem. These include debugging the ERHAM computer program necessary to fit the spectra and the free rotor to high barrier correlation diagram necessary to understand the torsional states of the four-fold rotor...
October 14, 2018: Journal of Chemical Physics
Wenlan Liu, Sofia Canola, Andreas Köhn, Bernd Engels, Fabrizia Negri, Reinhold F Fink
On the example of an aggregate of two perylenebisimide (PBI) molecules the character of the lowest excited electronic states in terms of charge transfer (CT) and Frenkel exciton (FE) configurations is investigated as a function of the intermolecular arrangement. A minimal model Hamiltonian based on two FE and two CT configurations at the frontier-orbitals CIS (FOCIS) level is shown to represent a simple and comprehensible approach providing insight into the physical significance of the model Hamiltonian matrix elements...
September 15, 2018: Journal of Computational Chemistry
Xiaolin Cai, Zhili Zhu, Weiyang Yu, Chunyao Niu, Jianjun Wang, Baoji Wang, Xiaohua Li, Liwei Zhang, Ruiqi Zhao, Yu Jia
On the basis of density functional theory (DFT) calculations, we propose a stable two-dimensional (2D) monolayer phosphorus carbide (PC) with a GaSe-like structure, which has intriguing electronic and optical properties. Our calculated results show that this 2D monolayer structure is more stable than the other allotropes predicted by Tománek et al. [ Nano Lett., 2016, 16, 3247⁻3252 ]. More importantly, this structure exhibits superb optical absorption, which can be mainly attributed to its direct band gap of 2...
October 11, 2018: Materials
V P Amin, J Zemen, M D Stiles
Transport calculations based on ab initio band structures reveal large interface-generated spin currents at Co/Pt, Co/Cu, and Pt/Cu interfaces. These spin currents are driven by in-plane electric fields but flow out of plane and can have similar strengths to spin currents generated by the spin Hall effect in bulk Pt. Each interface generates spin currents with polarization along z[over ^]×E, where z[over ^] is the interface normal and E denotes the electric field. The Co/Cu and Co/Pt interfaces additionally generate spin currents with polarization along m[over ^]×(z[over ^]×E), where m[over ^] gives the magnetization direction of Co...
September 28, 2018: Physical Review Letters
Peter B Karadakov, David L Cooper
It is shown, on the example of the monocyclic cyclononatetraenyl cation, C₉H₉+, that the fully-variational optimization of modern ab initio wavefunctions based on spin-coupled generalized valence bond (SCGVB) theory vindicates, in a surprising level of detail, essential features of Heilbronner's ideas for the electronic structure of Möbius annulenes such as the arrangement of overlapping carbon 2p atomic orbitals along a Möbius strip, leading to a phase inversion between the first and last orbitals. In the SCGVB description, the aromaticity of this Möbius system with eight π electrons follows from the extensive resonance between VB structures...
October 12, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Weiwei Yang, Kimberley N Poland, Steven R Davis
The isomerizations of 3,4-diazatricyclo[,7]hept-3-ene and 3,4-diazatricyclo[,7]heptane to their corresponding products were studied by ab initio calculations. Structures were determined at the multiconfiguration self-consistent field level and energies calculated at the single state second-order MRMP level. The isomerization of 3,4-diazatricyclo[,7]hept-3-ene occurs through four unique pathways with barriers of 36.1 and 37.9 kcal mol-1 for the allowed channels, while those for the forbidden channels were 44...
October 12, 2018: Physical Chemistry Chemical Physics: PCCP
Sean A Fischer, Brett I Dunlap, Daniel Gunlycke
The aqueous proton displays an anomalously large diffusion coefficient that is up to 7 times that of similarly sized cations. There is general consensus that the proton achieves its high diffusion through the Grotthuss mechanism, whereby protons hop from one molecule to the next. A main assumption concerning the extraction of the timescale of the Grotthuss mechanism from experimental results has been that, on average, there is an equal probability for the proton to hop to any of its neighboring water molecules...
September 21, 2018: Chemical Science
Markus Kubin, Meiyuan Guo, Thomas Kroll, Heike Löchel, Erik Källman, Michael L Baker, Rolf Mitzner, Sheraz Gul, Jan Kern, Alexander Föhlisch, Alexei Erko, Uwe Bergmann, Vittal Yachandra, Junko Yano, Marcus Lundberg, Philippe Wernet
Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando , is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state...
September 7, 2018: Chemical Science
Eva Perlt, Promit Ray, Andreas Hansen, Friedrich Malberg, Stefan Grimme, Barbara Kirchner
Ionic liquids raise interesting but complicated questions for theoretical investigations due to the fact that a number of different inter-molecular interactions, e.g., hydrogen bonding, long-range Coulomb interactions, and dispersion interactions, need to be described properly. Here, we present a detailed study on the ionic liquids ethylammonium nitrate and 1-ethyl-3-methylimidazolium acetate, in which we compare different dispersion corrected density functional approximations to accurate local coupled cluster data in static calculations on ionic liquid clusters...
May 21, 2018: Journal of Chemical Physics
Bikramjit Sharma, Amalendu Chandra
Gamma-aminobutyric acid (GABA), a primary neurotransmitter, accomplishes its activities by binding to different receptor sites in different conformations. It is known to have two major conformers: the closed and open forms. Earlier studies on preferred conformation of GABA in water revealed differing results with some reporting the open form while others inferring the closed form to be more stable. We found the existence of many open forms and only one closed form of GABA in water through ab initio metadynamics simulation...
May 21, 2018: Journal of Chemical Physics
Johannes Ingenmey, Michael von Domaros, Eva Perlt, Sergey P Verevkin, Barbara Kirchner
We applied the binary Quantum Cluster Equilibrium (bQCE) method to a number of alkylammonium-based protic ionic liquids in order to predict boiling points, vaporization enthalpies, and proton activities. The theory combines statistical thermodynamics of van-der-Waals-type clusters with ab initio quantum chemistry and yields the partition functions (and associated thermodynamic potentials) of binary mixtures over a wide range of thermodynamic phase points. Unlike conventional cluster approaches that are limited to the prediction of thermodynamic properties, dissociation reactions can be effortlessly included into the bQCE formalism, giving access to ionicities, as well...
May 21, 2018: Journal of Chemical Physics
Zhaoxu Wang, Yi Liu, Baishu Zheng, Fengxiang Zhou, Yinchun Jiao, Yuan Liu, XunLei Ding, Tian Lu
Intermolecular interaction of XH2 P···MY (X = H, CH3 , F, CN, NO2 ; M = Cu, Ag, Au; Y = F, Cl, Br, I) complexes was investigated by means of an ab initio method. The molecular interaction energies are in the order Ag < Cu < Au and increased with the decrease of RP···M . Interaction energies are strengthened when electron-donating substituents X connected to XH2 P, while electron-withdrawing substituents produce the opposite effect. The strongest P···M bond was found in CH3 H2 P···AuF with -70...
May 21, 2018: Journal of Chemical Physics
Brian Stankus, Nikola Zotev, David M Rogers, Yan Gao, Asami Odate, Adam Kirrander, Peter M Weber
The photodissociation dynamics of 1,4-diiodobenzene is investigated using ultrafast time-resolved photoelectron spectroscopy. Following excitation by laser pulses at 271 nm, the excited-state dynamics is probed by resonance-enhanced multiphoton ionization with 405 nm probe pulses. A progression of Rydberg states, which come into resonance sequentially, provide a fingerprint of the dissociation dynamics of the molecule. The initial excitation decays with a lifetime of 33 ± 4 fs, in good agreement with a previous study...
May 21, 2018: Journal of Chemical Physics
Yukio Watanabe
In the calculations of tetragonal BaTiO3 , some exchange-correlation (XC) energy functionals such as local density approximation (LDA) have shown good agreement with experiments at room temperature (RT), e.g., spontaneous polarization ( P S ), and superiority compared with other XC functionals. This is due to the error compensation of the RT effect and, hence, will be ineffective in the heavily strained case such as domain boundaries. Here, ferroelectrics under large strain at RT are approximated as those at 0 K because the strain effect surpasses the RT effects...
May 21, 2018: Journal of Chemical Physics
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