More Criegee Sightings The reaction of ozone with unsaturated hydrocarbons produces short-lived molecules termed intermediates. simplest such molecule, H 2 CO , was recently detected and monitored in the laboratory. Su et al. (p. 174 ; see Perspective by Vereecken ) have obtained its vibrational spectrum, which could ultimately enable direct measurements reactivity atmosphere. Taatjes 177 report on laboratory preparation next heavier intermediate, bears a methyl group place one hydrogen atoms.

Recently developed parameters for five first-row transition-metal elements (M = Sc, Ti, Fe, Co, and Ni) in combination with H, C, N, O as well the same metal (M-M) spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method have been calibrated. To test their performance a couple sets of compounds selected to represent variety interactions bonding schemes that occur frequently containing systems. The results show DFTB present most cases reproduces structural...

A new perturbation approach is proposed that enhances the low-order, perturbative convergence by modifying zeroth-order Hamiltonian in a manner enlarges any small-energy denominators may otherwise appear expansion. This intruder state avoidance (ISA) method can be used conjunction with approach, but most applicable to cases where small energy arise from orthogonal-space states-so-called states-that should, under normal circumstances, make negligible contribution target of interests. ISA...

Ammonia adsorption on single-walled carbon nanotubes (SWNTs) was studied by means of infrared spectroscopy at both cryogenic (approximately 94 K) and room 300 temperatures. At K, vacuum-annealed SWNTs showed no detectable ammonia uptake. However, the found to be sensitive functionalities defects nanotube surfaces. NH3 detected HNO3-treated nanotubes, characterized significant defects, prior vacuum annealing. desorbed from those above 140 indicating a weak adsorbate-nanotube interaction 30...

A parametrization scheme for the electronic part of density-functional based tight-binding (DFTB) method that covers periodic table is presented. semiautomatic has been developed uses Kohn-Sham energies and band structure curvatures real fictitious homoatomic crystal structures as reference data. confinement potential used to tighten orbitals, which includes two free parameters are optimize performance method. The tested on more than 100 systems shows excellent overall performance.

Abstract The Criegee intermediates are carbonyl oxides that play critical roles in ozonolysis of alkenes the atmosphere. So far, mid-infrared spectrum only simplest intermediate CH 2 OO has been reported. Methyl substitution produces two conformers 3 CHOO and consequently complicates infrared spectrum. Here we report transient syn - anti -CH CHOO, produced from CHI + O a flow reactor, using step-scan Fourier-transform spectrometer. Guided supported by high-level full-dimensional quantum...

We investigated IR spectra in the CH- and OH-stretching regions of size-selected methanol clusters, (CH(3)OH)(n) with n = 2-6, a pulsed supersonic jet by using IR-VUV (vacuum-ultraviolet) ionization technique. VUV emission at 118 nm served as source time-of-flight mass spectrometer. The tunable laser predissociation or excitation before ionization. variations intensity protonated cluster ions (CH(3)OH)(n)H(+) CH(3)OH(+) (CH(3)OH)(2)(+) were monitored light was tuned across range 2650-3750...

In this work, we derive and test a new automatized strategy to construct repulsive potentials for the self-consistent charge density functional tight-binding (SCC-DFTB) method. This approach allows one explore parameter space in systematic fashion order find optimal solutions. We that due limited flexibility of SCC-DFTB electronic part, not all properties can be optimized simultaneously. For example, optimization heats formation is conflict with vibrational frequencies. Therefore, special...

Nitrogen-bridged donor–acceptor multifused dithienopyrrolobenzothiadiazole (DTPBT) and dibenzothiadiazolopyrrolothiophene (DBTPT) were successfully synthesized by intramolecular Cadogan annulation. The electron-deficient benzothiadiazole unit in DTPBT can be converted to benzoselenadiazole quinoxaline moieties through reduction/cyclization generate dithienopyrrolobenzoselenadiazole (DTPBSe) dithienopyrroloquinoxaline (DTPQX), respectively. nitrogen atoms function as the bridges for covalent...

We present a novel density-functional tight-binding (DFTB) parametrization toolkit developed to optimize the parameters of various DFTB models in fully automatized fashion. The main features algorithm, based on particle swarm optimization technique, are discussed, and number initial pilot applications methodology molecular solid systems presented.

We present an algorithm for automatic computation of generalized Zhang-Zhang (GZZ) polynomials benzenoids. The Fortran 95 implementation the presented has been used determination GZZ several basic classes Correctness derived formulas demonstrated using standard decomposition recurrence relations.

We present a detailed study of harmonic vibrational frequencies obtained with the self-consistent charge density functional tight-binding (SCC-DFTB) method. Our testing set comprises 66 molecules and 1304 distinct modes. Harmonic are computed using an efficient analytical algorithm developed coded by authors. The results compared to experiment other theoretical findings. Scaling factor for SCC-DFTB method, determined minimization mean absolute deviation scaled frequencies, is found be...

Analytical formulation of the second-order geometrical derivatives energy for self-consistent-charge density-functional tight-binding (SCC-DFTB) method is presented. To test its quality and numerical performance, derived formalism has been coded applied calculation harmonic vibrational frequencies a set 17 small medium size molecules. For this set, average absolute deviation from experiment 99 cm−1 SCC-DFTB vs 62 Møller-Plesset perturbation theory with cc-pVDZ basis (MP2/cc-pVDZ) 32 B3LYP...

We employ the self-consistent-charge density-functional tight-binding (SCC-DFTB) method for computing geometric, electronic, and vibrational properties various topological isomers of small fullerenes. consider all 35 five- six-member rings containing fullerenes, C20, C24, C26, C28, C30, C32, C34, C36, as first part a larger effort to catalog CC distance distributions, valence CCC angle electronic densities states (DOSs), (VDOSs), infrared (IR) Raman spectra fullerenes C20-C180. Common...

We present a detailed analysis of the factors influencing formation epoxide and ether groups in graphene nanoflakes using conventional density functional theory (DFT), density-functional tight-binding (DFTB) method, π-Hückel theory, graph theoretical invariants. The relative thermodynamic stability associated with chemisorption oxygen atoms at various positions on hexagonal flakes (HGFs) D6h-symmetry is determined by two – viz. disruption π-conjugation HGF geometrical deformation structure....

We investigated the basis set convergence of high-order coupled-cluster interaction energy contributions for 21 small weakly bound complexes. By performing CCSDT(Q) calculations in at least aug-cc-pVTZ set, and CCSDT aug-cc-pVQZ (aug-cc-pVTZ one system), we found to be quite slow. In particular, 6-31G*(0.25) 6-31G**(0.25,0.15) bases advocated by Hobza et al. (J. Chem. Theory Comput. 2013, 9, 2151; ibid. 3420) are unsuitable post-CCSD(T) effects, with average errors CCSDT(Q)-CCSD(T)...

Schrödinger equation for harmonium and related models may be transformed to the biconfluent Heun equation. The solubility of this its applications in quantum chemistry are briefly discussed.

The lowest-lying excited states of N2 and CO are examined for the presence intruder that adversely influence perturbative convergence in computations using multireference Mo/ller–Plesset perturbation theory. Intruder found Πu3 state Π3 CO. Since, second order, these intruders—under normal circumstances—should make a negligible contribution to target state, their contributions second-order energies simply removed from expansion. With removed, vertical excitation (3Π) (CO) is only 0.23 eV...

Abstract A detailed analysis of a severe intruder state problem in the multistate multireference perturbation theory (MS‐MRPT) calculations on ground manganese dimer is presented. An enormous number detected states (> 5000) do not permit finding even an approximate shape X 1 Σ potential energy curve. The are explicitly demonstrated to originate from quasidegeneracies zeroth‐order Hamiltonian spectrum. electronic configurations responsible for appearance identified as single and double...

Prediction of a false ground state with popular variants multireference perturbation theory (CASPT2 and MRMP) is reported for remarkably simple chemical system: the Sc2 molecule.

Combined temperature-programmed desorption and IR studies suggest that absorption cross sections of IR-active vibrations molecules "strongly" bound to single-wall carbon nanotubes (SWCNTs) are reduced at least by a factor 10. Quantum chemical simulations show intensities endohedrally encapsulated dramatically reduced, identify dielectric screening highly polarizable SWCNT sidewalls as the origin such "screening". The observed intensity reduction originates from sizable cancellation adsorbate...

Structural characterization of nanodiamonds by vibrational spectroscopy requires knowledge the factors determining spectra. Raman is widely used to detect diamond phase in nanodiamond powders and films, but several spectral features are still poorly understood. Here we present a theoretical study evolution hydrocarbon spectra with increasing size, from adamantane molecule approximately 3 nm large tetrahedral octahedral particles T(d) symmetry, containing up about 1000 carbon atoms. The...

An extension of the self-consistent charge density-functional tight-binding (SCC-DFTB) method is presented that allows for calculating intensities peaks in vibrational Raman spectra very large molecules. The based on a simple ansatz: an extra term, which describes interaction external electric field with induced atomic charges, added to SCC-DFTB energy expression. We apply modified formalism reproducing 17 organic calculated are compared experiment and obtained from density functional theory...

The self-consistent charge density-functional tight-binding (SCC-DFTB) method is employed for studying various molecular properties of small fullerenes: C(28), C(60), and C(70). computed bond distances, vibrational infrared Raman spectra, densities states, electronic states are compared with experiment (where available) theory (DFT) calculations using basis sets. presented DFT benchmark the correlation-consistent polarized valence triple zeta set at present most extensive on harmonic...