Analytische Ableitungen der Energie für den "Equation-of-Motion-Coupled-Cluster"-Ansatz zur Berechnung von Ionisationspotentialen

In der vorliegenden Arbeit wird die Theorie der analytischen zweiten Ableitungen für die EOMIP-CCSD-Methode formuliert sowie die durchgeführte Implementierung im Quantenchemieprogramm CFOUR beschrieben. Diese Ableitungen sind von Bedeutung bei der Bestimmung statischer Polarisierbarkeiten und harmonischer Schwingungsfrequenzen und in dieser Arbeit wird die Genauigkeit des EOMIP-CCSD-Ansatzes bei der Berechnung dieser Eigenschaften für verschiedene radikalische Systeme untersucht. Des Weiteren können mit Hilfe der ersten und zweiten Ableitungen vibronische Kopplungsparameter berechnet werden, welche zur Simulation von Molekülspektren in Kombination mit dem Köppel-Domcke-Cederbaum (KDC)-Modell - in der Arbeit am Beispiel des Formyloxyl (HCO2)-Radikals demonstriert - benötigt werden.rnrnDer konzeptionell einfache EOMIP-CC-Ansatz wurde gewählt, da hier die Wellenfunktion eines Radikalsystems ausgehend von einem stabilen geschlossenschaligen Zustand durch die Entfernung eines Elektrons gebildet wird und somit die Problematik der Symmetriebrechung umgangen werden kann. Im Rahmen der Implementierung wurden neue Programmteile zur Lösung der erforderlichen Gleichungen für die gestörten EOMIP-CC-Amplituden und die gestörten Lagrange-Multiplikatoren zeta zum Quantenchemieprogramm CFOUR hinzugefügt. Die unter Verwendung des Programms bestimmten Eigenschaften werden hinsichtlich ihrer Leistungsfähigkeit im Vergleich zu etablierten Methoden wie z.B. CCSD(T) untersucht. Bei der Berechnung von Polarisierbarkeiten und harmonischen Schwingungsfrequenzen liefert die EOMIP-CCSD-Theorie meist gute Resultate, welche nur wenig von den CCSD(T)-Ergebnissen abweichen. Einzig bei der Betrachtung von Radikalen, für die die entsprechenden Anionen nicht stabil sind (z.B. NH2⁻ und CH3⁻), liefert der EOMIP-CCSD-Ansatz aufgrund methodischer Nachteile keine aussagekräftige Beschreibung. rnrnDie Ableitungen der EOMIP-CCSD-Energie lassen sich auch zur Simulation vibronischer Kopplungen innerhalb des KDC-Modells einsetzen.rnZur Kopplung verschiedener radikalischer Zustände in einem solchen Modellpotential spielen vor allem die Ableitungen von Übergangsmatrixelementen eine wichtige Rolle. Diese sogenannten Kopplungskonstanten können in der EOMIP-CC-Theorie besonders leicht definiert und berechnet werden. Bei der Betrachtung des Photoelektronenspektrums von HCO2⁻ werden zwei Alternativen untersucht: Die vertikale Bestimmung an der Gleichgewichtsgeometrie des HCO2⁻-Anions und die Ermittlung adiabatischer Kraftkonstanten an den Gleichgewichtsgeometrien des Radikals. Lediglich das adiabatische Modell liefert bei Beschränkung auf harmonische Kraftkonstanten eine qualitativ sinnvolle Beschreibung des Spektrums. Erweitert man beide Modelle um kubische und quartische Kraftkonstanten, so nähern sich diese einander an und ermöglichen eine vollständige Zuordnung des gemessenen Spektrums innerhalb der ersten 1500 cm⁻¹. Die adiabatische Darstellung erreicht dabei nahezu quantitative Genauigkeit.

Optisch detektierte Magnetresonanz an NV-Zentren in Diamant

Die rasante Entwicklung der Computerindustrie durch die stetige Verkleinerung der Transistoren führt immer schneller zum Erreichen der Grenze der Si-Technologie, ab der die Tunnelprozesse in den Transistoren ihre weitere Verkleinerung und Erhöhung ihrer Dichte in den Prozessoren nicht mehr zulassen. Die Zukunft der Computertechnologie liegt in der Verarbeitung der Quanteninformation. Für die Entwicklung von Quantencomputern ist die Detektion und gezielte Manipulation einzelner Spins in Festkörpern von größter Bedeutung. Die Standardmethoden der Spindetektion, wie ESR, erlauben jedoch nur die Detektion von Spinensembles. Die Idee, die das Auslesen von einzelnen Spins ermöglich sollte, besteht darin, die Manipulation getrennt von der Detektion auszuführen.rn Bei dem NV−-Zentrum handelt es sich um eine spezielle Gitterfehlstelle im Diamant, die sich als einen atomaren, optisch auslesbaren Magnetfeldsensor benutzen lässt. Durch die Messung seiner Fluoreszenz sollte es möglich sein die Manipulation anderer, optisch nicht detektierbaren, “Dunkelspins“ in unmittelbarer Nähe des NV-Zentrums mittels der Spin-Spin-Kopplung zu detektieren. Das vorgeschlagene Modell des Quantencomputers basiert auf dem in SWCNT eingeschlossenen N@C60.Die Peapods, wie die Einheiten aus den in Kohlenstoffnanoröhre gepackten Fullerenen mit eingefangenem Stickstoff genannt werden, sollen die Grundlage für die Recheneinheiten eines wahren skalierbaren Quantencomputers bilden. Die in ihnen mit dem Stickstoff-Elektronenspin durchgeführten Rechnungen sollen mit den oberflächennahen NV-Zentren (von Diamantplatten), über denen sie positioniert sein sollen, optisch ausgelesen werden.rnrnDie vorliegende Arbeit hatte das primäre Ziel, die Kopplung der oberflächennahen NV-Einzelzentren an die optisch nicht detektierbaren Spins der Radikal-Moleküle auf der Diamantoberfläche mittels der ODMR-Kopplungsexperimente optisch zu detektieren und damit entscheidende Schritte auf dem Wege der Realisierung eines Quantenregisters zu tun.rn Es wurde ein sich im Entwicklungsstadium befindende ODMR-Setup wieder aufgebaut und seine bisherige Funktionsweise wurde an kommerziellen NV-Zentrum-reichen Nanodiamanten verifiziert. Im nächsten Schritt wurde die Effektivität und Weise der Messung an die Detektion und Manipulation der oberflächennah (< 7 nm Tiefe) implantieren NV-Einzelzenten in Diamantplatten angepasst.Ein sehr großer Teil der Arbeit, der hier nur bedingt beschrieben werden kann, bestand aus derrnAnpassung der existierenden Steuersoftware an die Problematik der praktischen Messung. Anschließend wurde die korrekte Funktion aller implementierten Pulssequenzen und anderer Software-Verbesserungen durch die Messung an oberflächennah implantierten NV-Einzelzentren verifiziert. Auch wurde der Messplatz um die zur Messung der Doppelresonanz notwendigen Komponenten wie einen steuerbaren Elektromagneten und RF-Signalquelle erweitert. Unter der Berücksichtigung der thermischen Stabilität von N@C60 wurde für zukünftige Experimente auch ein optischer Kryostat geplant, gebaut, in das Setup integriert und charakterisiert.rn Die Spin-Spin-Kopplungsexperimente wurden mit dem sauerstoffstabilen Galvinoxyl-Radikalals einem Modell-System für Kopplung durchgeführt. Dabei wurde über die Kopplung mit einem NVZentrum das RF-Spektrum des gekoppelten Radikal-Spins beobachtet. Auch konnte von dem gekoppelten Spin eine Rabi-Nutation aufgenommen werden.rn Es wurden auch weitere Aspekte der Peapod Messung und Oberflächenimplantation betrachtet.Es wurde untersucht, ob sich die NV-Detektion durch die SWCNTs, Peapods oder Fullerene stören lässt. Es zeigte sich, dass die Komponenten des geplanten Quantencomputers, bis auf die C60-Cluster, für eine ODMR-Messanordnung nicht detektierbar sind und die NV-Messung nicht stören werden. Es wurde auch betrachtet, welche Arten von kommerziellen Diamantplatten für die Oberflächenimplantation geeignet sind, für die Kopplungsmessungen geeignete Dichte der implantierten NV-Zentren abgeschätzt und eine Implantation mit abgeschätzter Dichte betrachtet.

Accordion-optimized DEPT experiments

In this contribution, a pulse sequence is described for recording accordion-optimized DEPT experiments. The proposed ACCORDEPT experiment detects a wide range of one-bond coupling constants using accordion optimization. As a proof of concept, this strategy has been applied to a mesogen containing a large range of one-bond (1)J(CH) coupling constants associated with the various structural elements. The ACCORDEPT experiment afforded significant enhancements for the resonances with the larger 1JCH couplings, similar SNR for aliphatic resonances, but reduced SNR for aliphatic resonances as compared with the standard DEPT experiment. In addition, the ACCORDEPT is straightforward to implement, does not require any supplementary calibration procedures and can be used under automated conditions without difficulty by inexperienced users. Copyright (C) 2010 John Wiley & Sons, Ltd.

Stereoselectivity of Additions to N-Methyl Acetonitrilium Fluorosulfonate

Alkoxy-N-methyl-acetiminium salts were prepared by addition of CH3OH and C2H5OH to N-methyl acetonitrilium fluorosulfonate at low temperature. Analysis of the (5)J(HH) and (3)J(13)C-H coupling constants in the NMR spectra showed an anti addition with a diastereoselectivity of >9596. Deprotonation of these salts with (Z)-configuration gave the corresponding N-methyl-alkoxyacetimines with very high (E)-configuration. Upon protonation at -78 degrees C, these iminoesters gave the corresponding alkoxy-N-methyl-acetirninium salts with (E)-configuration. Computational analyses of the iminoesters and the corresponding iminium cations including the conformations give insight into the relative stability. Nitrilium salts can be used as reagents, exemplified by some esterifications between simple acids and alcohols.

O(N) Models with Topological Lattice Actions

A variety of lattice discretisations of continuum actions has been considered, usually requiring the correct classical continuum limit. Here we discuss “weird” lattice formulations without that property, namely lattice actions that are invariant under most continuous deformations of the field configuration, in one version even without any coupling constants. It turns out that universality is powerful enough to still provide the correct quantum continuum limit, despite the absence of a classical limit, or a perturbative expansion. We demonstrate this for a set of O(N) models (or non-linear σ-models). Amazingly, such “weird” lattice actions are not only in the right universality class, but some of them even have practical benefits, in particular an excellent scaling behaviour.

Probing the Structure, Pseudorotation, and Radial Vibrations of Cyclopentane by Femtosecond Rotational Raman Coherence Spectroscopy

Femtosecond time-resolved Raman rotational coherence spectroscopy (RCS) is employed to determine accurate rotational, vibration–rotation coupling constants, and centrifugal distortion constants of cyclopentane (C⁵H¹⁰). Its lowest-frequency vibration is a pseudorotating ring deformation that interconverts 10 permutationally distinct but energetically degenerate “twist” minima interspersed by 10 “bent” conformers. While the individual twist and bent structures are polar asymmetric tops, the pseudorotation is fast on the time scale of external rotation, rendering cyclopentane a fluxionally nonpolar symmetric top molecule. The pseudorotational level pattern corresponds to a one-dimensional internal rotor with a pseudorotation constant Bps ≈ 2.8 cm⁻¹. The pseudorotational levels are significantly populated up to l = ± 13 at 298 K; <10% of the molecules are in the l = 0 level. The next-higher vibration is the “radial” ν²³ ring deformation mode at 273 cm⁻¹, which is far above the pseudorotational fundamental. Femtosecond Raman RCS measurements were performed in a gas cell at T = 293 K and in a pulsed supersonic jet at T ≈ 90 K. The jet cooling reduces the pseudorotational distribution to l < ±8 and eliminates the population of ν²³, allowing one to determine the rotational constant as A0 = B0 = 6484.930(11) MHz. This value is ∼300 times more precise than the previous value. The fit of the RCS transients reveals that the rotation–pseudorotation coupling constant αe,psB = −0.00070(1) MHz is diminutive, implying that excitation of the pseudorotation has virtually no effect on the B0 rotational constant of cyclopentane. The smallness of αe,psB can be realized when comparing to the vibration–rotation coupling constant of the ν²³ vibration, αe,23B = −9.547(1) MHz, which is about 10⁴ times larger.

Finite volume effects in chiral perturbation theory with twisted boundary conditions

We study the effects of a finite cubic volume with twisted boundary conditions on pseudoscalar mesons. We apply Chiral Perturbation Theory in the p-regime and introduce the twist by means of a constant vector field. The corrections of masses, decay constants, pseudoscalar coupling constants and form factors are calculated at next-to-leading order. We detail the derivations and compare with results available in the literature. In some case there is disagreement due to a different treatment of new extra terms generated from the breaking of the cubic invariance. We advocate to treat such terms as renormalization terms of the twisting angles and reabsorb them in the on-shell conditions. We confirm that the corrections of masses, decay constants, pseudoscalar coupling constants are related by means of chiral Ward identities. Furthermore, we show that the matrix elements of the scalar (resp. vector) form factor satisfies the Feynman–Hellman Theorem (resp. the Ward–Takahashi identity). To show the Ward–Takahashi identity we construct an effective field theory for charged pions which is invariant under electromagnetic gauge transformations and which reproduces the results obtained with Chiral Perturbation Theory at a vanishing momentum transfer. This generalizes considerations previously published for periodic boundary conditions to twisted boundary conditions. Another method to estimate the corrections in finite volume are asymptotic formulae. Asymptotic formulae were introduced by Lüscher and relate the corrections of a given physical quantity to an integral of a specific amplitude, evaluated in infinite volume. Here, we revise the original derivation of Lüscher and generalize it to finite volume with twisted boundary conditions. In some cases, the derivation involves complications due to extra terms generated from the breaking of the cubic invariance. We isolate such terms and treat them as renormalization terms just as done before. In that way, we derive asymptotic formulae for masses, decay constants, pseudoscalar coupling constants and scalar form factors. At the same time, we derive also asymptotic formulae for renormalization terms. We apply all these formulae in combination with Chiral Perturbation Theory and estimate the corrections beyond next-to-leading order. We show that asymptotic formulae for masses, decay constants, pseudoscalar coupling constants are related by means of chiral Ward identities. A similar relation connects in an independent way asymptotic formulae for renormalization terms. We check these relations for charged pions through a direct calculation. To conclude, a numerical analysis quantifies the importance of finite volume corrections at next-to-leading order and beyond. We perform a generic Analysis and illustrate two possible applications to real simulations.

Arrays de sensores interferométricos recirculantes de fibra óptica

Two discrete interferometric sensors' arrays have been analysed from time división multiplexing of recirculating crossed loop structures based on singlemode optical fiber. Intensity impulsive responses for both arrays have been obtained and compared under different design considerations, calculating Ihe system coupling constants, signial to interference noise ratio, input pulse repetition rate and duty cycle for each case. First experimental results are shown in this paper and very simple temperature and pressure sensing applicalions are suggested from here.

New methods of structure refinement for macromolecular structure determination by NMR

Recent advances in multidimensional NMR methodology have permitted solution structures of proteins in excess of 250 residues to be solved. In this paper, we discuss several methods of structure refinement that promise to increase the accuracy of macromolecular structures determined by NMR. These methods include the use of a conformational database potential and direct refinement against three-bond coupling constants, secondary 13C shifts, 1H shifts, T1/T2 ratios, and residual dipolar couplings. The latter two measurements provide long range restraints that are not accessible by other solution NMR parameters.

Propriedades fotoquímicas de alguns complexos de ferro(II) e rênio(I)

Neste trabalho, foram estudadas as propriedades fotoquímica e/ou fotofísica de alguns compostos de coordenação de rênio(l) e ferro(I I). A irradiação dos complexos fac-[Re(CO)3(NN)(trans-L)]+, NN= 4,7-difenil-1,10- fenantrolina (ph2phen) ou 5-cloro-1,10-fenantrolina (Clphen) e L = 1,2-bis(4-piridil)etileno (bpe) ou 4-estirilpiridina (stpy), em acetonitrila ou em filme de poli(metacrilato de metila) (PMMA) resulta em variações espectrais condizentes com a fotoisomerização trans-cis do ligante coordenado. A determinação dos rendimentos quânticos para a fotorreação pela variação espectral resultou em valores aparentes, uma vez que o reagente e o fotoproduto absorvem na mesma região. Para a determinação do rendimento quântico real, Φreal, utilizou-se a técnica de 1H RMN, na qual os sinais do fotoproduto e do reagente são observados em regiões distintas com diferentes constantes de acoplamento. Os valores de Φreal obtidos para fac-[Re(CO)3h(NN)(trans-bpe)]+ (ph2phen: Φ313= 0,43 ± 0,03; Φ365= 0,44 ± 0,02; Φ404= 0,43 ± 0,02; Clphen: Φ313= 0,56 ± 0,03; Φ365= 0,55 ± 0,04; Φ404= 0,57 ± 0,06) são independentes do comprimento de onda de irradiação, indicando a existência de um único canal para a população do estado excitado 3ILtrans-bpe. Por outro lado, para fac-[Re(CO)3(NN)(trans-stpy)]+, os valores de Φreal sob irradiação a 404 nm são menores que os determinados para os demais comprimentos de onda de irradiação (ph2phen: Φ313= 0,60 ± 0,05; Φ365= 0,64 ± 0,09; Φ404= 0,42 ± 0,03; Clphen: Φ313= 0,52 ± 0,05; Φ365= 0,58 ± 0,02; Φ404= 0,41 ± 0,06), indicando que, a energias maiores, em que o Iigante absorve significativamente, deve existir a contribuição de outro canal para a população do estado excitado 3ILtrans-stpy. A eficiência do fotoprocesso foi avaliada por meio da substituição dos ligantes NN e/ou L, e a diferença nos valores de Φreal entre os complexos deve estar relacionada principalmente com as distintas eficiências de cruzamento intersistemas. o fotoprocesso altera as propriedades fotofísicas desses complexos. Os isômeros trans apresentam fraca ou nenhuma emissão a 298 K, enquanto os fotoprodutos, fac-[Re(CO)3(NN)(cis-L)]+, apresentam intensa luminescência dominada pelo estado excitado 3MLCTRe→NN, que é sensivel à rigidez do meio. A reatividade fotoquímica dos pentacianoferratos(II) [Fe(CN)5 (NN)]3-, NN= 2aminobenzilamina (aba), 2-aminobenzamida (ab), 2-(dimetilaminometil)-3-hidroxipiridina (dmampy), 2-aminometilpiridina (ampy), 2-aminoetilpiridina (aepy) ou 2-(2metilaminoetil) piridina (maepy), também foi investigada. A irradiação desses complexos resulta na fotossubstituição do CN-, a qual só pode ser detectada quando o ligante possui um segundo grupo coordenante nas proximidades da esfera de coordenação. Os rendimentos quânticos da fotossubstituição são dependentes do comprimento de onda de irradiação (Φ313= 0,13 ± 0,01; Φ334= 0,091 ± 0,001; Φ365= 0,056 ± 0,002; Φ404= 0,022 ± 0,002; Φ436= 0,015 ± 0,001, por exemplo, para NN = aba) e indicam a existência de canais distintos pelos quais a fotorreação ocorre ou as diferentes eficiências de cruzamento intersistema para a população do estado excitado reativo. A eficiência do fotoprocesso também depende do Iigante utilizado (λirr= 365 nm: Φaba= 0,056, Φab= 0,14, Φampy= 0,046, Φaepy= 0,066, Φmaepy= 0,069 e Φdmampy= 0,12). Na série das diaminas, o rendimento quântico é maior para [Fe(CN)5(ab)]3-, que possui dois sítios para ocorrer o fechamento do anel. Na série das aminopiridinas, observa-se a influência do comprimento da cadeia na eficiência do fechamento do anel. A presença de metilas ligadas ao nitrogênio alifático deve ter pouca ou nenhuma influência na eficiência do fotoprocesso.

The emergence of classical behaviour in magnetic adatoms

A wide class of nanomagnets shows striking quantum behaviour, known as quantum spin tunnelling (QST): instead of two degenerate ground states with opposite magnetizations, a bonding-antibonding pair forms, resulting in a splitting of the ground-state doublet with wave functions linear combination of two classically opposite magnetic states, leading to the quenching of their magnetic moment. Here we study how QST is destroyed and classical behaviour emerges in the case of magnetic adatoms, where, contrary to larger nanomagnets, the QST splitting is in some instances bigger than temperature and broadening. We analyze two different mechanisms for the renormalization of the QST splitting: Heisenberg exchange between different atoms, and Kondo exchange interaction with the substrate electrons. Sufficiently strong spin-substrate and spin-spin coupling renormalize the QST splitting to zero allowing the environmental decoherence to eliminate superpositions between classical states, leading to the emergence of spontaneous magnetization. Importantly, we extract the strength of the Kondo exchange for various experiments on individual adatoms and construct a phase diagram for the classical to quantum transition.

Structure of Petunia hybrida Defensin 1, a Novel Plant Defensin with Five Disulfide Bonds

The structure of a novel plant defensin isolated from the flowers of Petunia hybrida has been determined by H-1 NMR spectroscopy. P. hybrida defensin 1 (PhD1) is a basic, cysteine-rich, antifungal protein of 47 residues and is the first example of a new subclass of plant defensins with five disulfide bonds whose structure has been determined. PhD1 has the fold of the cysteine-stabilized alphabeta motif, consisting of an alpha-helix and a triple-stranded antiparallel beta-sheet, except that it contains a fifth disulfide bond from the first loop to the alpha-helix. The additional disulfide bond is accommodated in PhD1 without any alteration of its tertiary structure with respect to other plant defensins. Comparison of its structure with those of classic, four-disulfide defensins has allowed us to identify a previously unrecognized hydrogen bond network that is integral to structure stabilization in the family.

Metal Clips Induce Folding of a Short Unstructured Peptide into an a-Helix via Turn Conformations in Water. Kinetic versus Thermodynamic Products

Short peptides corresponding to two to four a-helical turns of proteins are not thermodynamically stable helices in water. Unstructured octapeptide Ac-His1*-Ala2-Ala3-His4*-His5*-Glu6-Leu7-His8*-NH2 (1) reacts with two [Pd ((NH2)-N-15(CH2)(2) (NH2)-N-15)(NO3)(2)] in water to form a kinetically stable intermediate, [{Pden}(2)-{(1,4)(5,8)-peptide}](2), in which two 19-membered metallocyclic rings stabilize two peptide turns. Slow subsequent folding to a thermodynamically more stable two-turn a-helix drives the equilibrium to [{Pden}(2)-{(1,5)(4,8)-peptide}] (3), featuring two 22-membered rings. This transformation from unstructured peptide via turns to an a-helix suggests that metal clips might be useful probes for investigating peptide folding.

Isolation, solution structure, and insecticidal activity of Kalata B2, a circular protein with a twist: Do Mobius strips exist in nature?

A large number of macrocyclic miniproteins with diverse biological activities have been isolated from the Rubiaceae, Violaceae, and Cucurbitaceae plant families in recent years. Here we report the three-dimensional structure determined using H-1 NMR spectroscopy and demonstrate potent insecticidal activity for one of these peptides, kalata B2. This peptide is one of the major components of an extract from the leaves of the plant Oldenlandia affinis. The structure consists of a distorted triple-stranded beta-sheet and a cystine knot arrangement of the disulfide bonds and is similar to those described for other members of the cyclotide family. The unique cyclic and knotted nature of these molecules makes them a fascinating example of topologically complex proteins. Examination of the sequences reveals that they can be separated into two subfamilies, one of which contains a larger number of positively charged residues and has a bracelet-like circularization of the backbone. The second subfamily contains a backbone twist due to a cis-peptidyl-proline bond and may conceptually be regarded as a molecular Mobius strip. Kalata B2 is the second putative member of the Mobius cyclotide family to be structurally characterized and has a cis-peptidyl-proline bond, thus validating the suggested name for this subfamily of cyclotides. The observation that kalata B2 inhibits the growth and development of Helicoverpa armigera larvae suggests a role for the cyclotides in plant defense. A comparison of the sequences and structures of kalata B1 and B2 provides insight into the biological activity of these peptides.