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We present a periodic/finite-cluster interface for fragment-based direct local ring-coupled-cluster doubles (d-LrCCD) calculations embedded in the periodic mean field. The fragment is defined by a set of Wannier functions (WFs), obtained from a periodic Hartree–Fock calculation. The pair-specific virtual space is spanned by projected atomic orbitals (PAOs) truncated to pair domains. The computational procedure is initiated by a periodic local Møller–Plesset (LMP2) calculation. A subset of the WF pairs is then subsequently subjected to a finite-cluster d-LrCCD treatment using the local coupled cluster program of Molpro; this subset is specified by an interorbital cutoff distance. The orbital, pair, and domain lists, as well as other essential quantities needed for d-LrCCD such as the Fock and overlap matrices, and the electron repulsion integrals (ERIs) in the basis of WFs and PAOs are evaluated in the periodic framework and passed to Molprovia an interface. These periodic quantities provide the correct periodic mean-field embedding for the fragment d-LrCCD. Moreover, no expensive orbital transformations involving orbital coefficients related to large supporting clusters are necessary. ERIs appearing in the d-LrCCD diagrams are factorized via density fitting, which enables an efficient processing of the corresponding terms via three-index intermediates. The corresponding 3-index and the metric 2-index ERIs involving auxiliary functions are also computed and transformed to the WF-PAO basis (the 3-index ERI) on the periodic side. Although the direct ring-CCD method itself is not generally more accurate than MP2, it is more stable in the case of small band gap systems, as it sums up the ring diagrams to infinite order. Furthermore, this interface is a first step toward a high-level fragment-based quantum chemical treatment such as local CCSD(T) within a periodic embedding that is treated at a lower level. As two test examples we study the physisorption of H2and argon on graphane.

This article reviews the periodic LMP2 method and its implementation in the CRYSCOR code. The main steps of the LMP2 calculations and the techniques employed are briefly described. Illustrative single-point calculations for three TiO2polymorphs: rutile, anatase and brookite in their experimental geometry are performed. It is shown that the method scales linearly with respect to the number of atoms per unit cell, and can be applied to relatively complex periodic systems. The LMP2 method in contrast to DFT positions rutile slightly lower in the energy than anatase. Brookite is found to be the most stable. However, since the energy differences are relatively small, a further investigation of the influence of the domain-sizes, geometry, zero-point vibrations, etc.on the relative stability of these systems is required.

The new, Laplace transform based multi-state local CC2 response method is compared to the previous single-state approach. The new method employs adaptive state specific local approximations for the eigenvectors of the Jacobian. As a result, it is much less dependent on the initial un-truncated CCS wavefunction and able to locate the relevant eigenstates also in difficult cases where the initial CCS eigenvectors are qualitatively wrong and where the original single-state method failed. In this paper we compare excitation energies, transition strengths, and dipole moments of the individual local approaches and the canonical reference calculation, for a set of different molecules and excited states.

Phosphorus sulfide cages α‐P4S4, α‐P4S5, β‐P4S5, and β‐P4S6and transition‐metal chlorides TaCl5and NbCl5form molecular adducts in CS2/n‐hexane. The crystal structures of the adducts (TaCl5)(α‐P4S4), (TaCl5)(α‐P4S5), (TaCl5)(β‐P4S5), (NbCl5)(β‐P4S5), and (TaCl5)(β‐P4S6) are reported and their conformation and energetic stability are discussed on the basis of ab initio electronic structure calculations. Furthermore bond lengths of coordinated and noncoordinated phosphorus sulfide cages obtained from experiment and theory are compared, emphasizing the changes within the cages that emerge upon coordination.

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By micro-histological analysis of plant remains in faecal pellets, we studied the diet of red deer Cervus elaphusduring a summer season in the subalpine zone of the Swiss National Park in the eastern Swiss Alps. Hitherto, very little quantitative information on the diet of Alpine red deer populations has been published. Faecal species composition was found to conform to the general pattern known from elsewhere: it was dominated by graminoids with dwarf shrubs (mainly Erica camea)as a strong secondary component and forbs and coniferous browse in minor proportions. Practically all pellet samples contained food obtained both from pastures and forests, irrespectively of where the pellets were collected. Although forest plants contributed 28% of the fragment numbers and 41% of the fragment area in the pellets, coniferous tree browse accounted for only 2.5 and 5.0%, respectively. This supports the findings of other studies that red deer most likely has little impact on the forest dynamics in the Park. The spatial uniformity of faeces composition did not reflect the substantial differences in grassland vegetation between three study areas, probably because deer locally selected nutritious graminoids (particularly red fescue Festuca rubra) at patch level.

Since traditional agriculture and forestry are no longer economically viable in many regions of the European Alps, subalpine forests will become less managed or completely abandoned in the near future. Therefore, the interest in understanding how forest stands will develop after abandonment has increased considerably over the past two decades. While much is known about stand structure and stand development of Norway spruce (Picea abiesL.) forests, almost no knowledge is available about the same processes in forest communities of the Central Alps. In the Swiss National Park (SNP), the forested area is comprised of mountain pine (Pinus montanaMiller), Swiss stone pine/larch, (Pinus cembraL./Larix deciduaL.). and mixed stands. When the Park was founded in 1914 all management activities were stopped. Therefore, this area offers the opportunity to study stand development and changes in stand structure after abandonment. We compared historic (1957) and present data (2001/02) from 19 stands that were grouped into characteristic stand types: “mountain pine”, “mixed”, and “stone pine”. We detected significant decreases in total tree density (stem/ha) and sapling density (saplings/ha) of 45 to 57%, and 64 to 76%, respectively, over the 45 years of observation for all stand types. These changes were strongly related to decreases in the number of shade intolerant mountain pine trees. Simultaneously, the amount of non-standing woody residue increased from less than 4 t/ha to 36 to67.7 t/ha, and the density of standing dead wood (stems/ha) decreased significantly between 72 and 94%. The biomass of standing dead wood (t/ha), however, changed only slightly between 1957 and 01/02. Our results describe the successional development of continental subalpine forests after abandonment and outlines changes that might take place in similar areas in the near future. Die traditionelle land- und forstwirtschaftliche Nutzung dürfte im Alpenraum in der näheren Zukunft wirtschaftlich bedingt immer häufiger aufgegeben werden. Dieser Trend wird mit großer Wahrscheinlichkeit die Dynamik von Gebirgsökosystemen und damit das Landschaftsbild stark beeinflussen. Aus diesem Grund stieg in den letzten Jahrzehnten das Interesse, die Sukzession auf nicht mehr bewirtschafteten Flächen zu verstehen. Die Bestandesstruktur und -entwicklung von subalpinen Fichtenwäldern (Picea abiesL.) wurde bereits intensiv untersucht; über Entwicklungsprozesse in zentralalpinen Bergföhren- (Pinus montanaMiller) und Arven-/Lärchenwälder (Pinus cembraL./Larix deciduaL.) ist hingegen nur wenig bekannt. Der seit 1914 vom Menschen nur noch touristisch genutzte Schweizerische Nationalpark (SNP) ist eines der wenigen Gebiete in Westeuropa, welches über längere Zeit nicht bewirtschaftet wurde. Der Park bietet daher die einzigartige Möglichkeit, die Veränderungen in Bestandesstruktur und -zusammensetzung nach Bewirtschaftungsaufgabe zu beobachten. Wir verglichen historische (1957) und aktuelle (2001/02) Daten von 19 Beständen, welche zu drei verschiedenen Bestandestypen gehören: „Bergföhre“, „Mischbestand“ und „Arve“. In den letzten 45 Jahren nahm die totale Stammzahl in allen drei Bestandestypen um 45 bis 57% und die Jungbaumzahl pro Hektar um 64 bis 76% signifikant ab, was vor allem auf den starken Rückgang der lichtbedürftigen Bergföhre zurückzuführen ist. Parallel zu dieser Entwicklung, nahm die Menge an liegendem Totholz in allen Bestandestypen von weniger als 4 t/ha auf 36 bis 67,7 t/ha zu, während die Anzahl toter Bäume pro Hektar um 72 bis 94% abnahm. Die Biomasse des stehenden Totholzes (t/ha) hat sich hingegen nur leicht verändert. Unsere Resultate beschreiben die sukzessionale Entwicklung von subalpinen Wäldern der Zentralalpen und zeigen, wie sich Wälder in ähnlichen Berggebieten in der nahen Zukunft entwickeln könnten.

Die Dichtefunktionaltheorie zielt auf die Beschreibung von Energieaufspaltungen von Spinzuständen und Spin‐Spin‐Kopplungen in Übergangsmetallkomplexen. Moleküldynamik‐Simulationen profitieren von verbesserten Referenzdaten und wachsenden Rechenkapazitäten; polarisierbare Kraftfelder sind auf dem Vormarsch. Mit linear skalierenden Algorithmen sind nun für große Moleküle korrelierte Elektronenstrukturrechungen möglich. Die Dichtefunktionaltheorie zielt verstärkt auf Übergangsmetallkomplexe. Bei Moleküldynamik‐Simulationen sind polarisierbare Kraftfelder auf dem Vormarsch. Für große Moleküle sind nun auch korrelierte Elektronenstrukturrechungen möglich.

The density fitting approximation is applied to the most expensive class of 2-electron integrals in local CCSD, i.e., to those integrals that involve four virtual orbitals (or projected AOs). The fitting error in the correlation energy is systematic and considerably smaller than the deviation between the local and the canonical CCSD energy. In order to restore O(N) scaling locality must be exploited for the fitting functions as well as for orbitals. Local fitting domains specified for individual centre pairs provide an adequate basis for such a local description, however, Dunlap's robust formula for the approximate integrals then no longer simplifies to the usual expression known as the V approximation. A symmetric formula is proposed as an alternative, which, although formally non-robust, yields virtually the same results as the robust formalism. The additional fitting error due to the introduction of local fitting domains is considerably smaller than the original fitting error itself (by at least an order of magnitude). Test calculations demonstrate O(N) scaling for the new LDF-LCCSD method. The approximate calculation of the 4-external integrals via density fitting in LDF-LCCSD is 10–100 times faster than the exact calculation via the O(N) 4-index transformation in LCCSD.

The density fitting approximation is applied to the most expensive class of 2-electron integrals in local CCSD, i.e., to those integrals that involve four virtual orbitals or projected AOs. The fitting error in the correlation energy is systematic and considerably smaller than the deviation between the local and the canonical CCSD energy. In order to restore scaling locality must be exploited for the fitting functions as well as for orbitals. Local fitting domains specified for individual centre pairs provide an adequate basis for such a local description, however, Dunlap's robust formula for the approximate integrals then no longer simplifies to the usual expression known as the Vapproximation. A symmetric formula is proposed as an alternative, which, although formally non-robust, yields virtually the same results as the robust formalism. The additional fitting error due to the introduction of local fitting domains is considerably smaller than the original fitting error itself by at least an order of magnitude. Test calculations demonstrate scaling for the new LDF-LCCSD method. The approximate calculation of the 4-external integrals viadensity fitting in LDF-LCCSD is 10–100 times faster than the exact calculation viathe 4-index transformation in LCCSD.

A new way to compute the external exchange matrices in the local coupled cluster (LCC) theory is presented, which eliminates the most important bottleneck of our previous linear scaling LCC methods. It is based on a decomposition of the transformed two-electron integral set involving four external indices into blocks belonging to quadruples of atoms. A new additional transformation module was developed, which generates this very compact 4-external integral set before the LCC iteration loop is entered. The length of this integral set and the computational cost for producing it scale linearly with molecular size. Using these precomputed integrals, their contraction with the amplitudes, i.e. the assembly of the external exchange matrices occurring in each LCC iteration now is performed directly in the (external) space of the projected AOs (AOs, atomic orbitals) rather than in AO basis as previously, and proceeds exceedingly fast (3 min compared to 15 h with our previous algorithm, for the largest test-molecule considered in this paper).

Energy partitioning schemes have been used to investigate the metallophilic attraction between gold, silver and copper atoms in model dimers of H–M–PH₃ and Cl–M–PH₃ type. Attraction between the monomers is found to be largest for M = Au, but the reduction from Au to Ag (Cu) is not more than 10–20% (25–35%). Equilibrium M–M distances, r_e(M–M), decrease by 0.2–0.3 Å from Au to Cu, and by 0.1–0.2 Å from Cl to H. An analysis of the intermolecular interaction energy shows that at r_e(M–M) dispersive and non-dispersive components are about equally important for all systems considered. However, the contribution due to metal nd–nd interaction falls drastically from 43% (35%) for Au, over 30% (27%) for Ag, to 18% (13%) for Cu in the H (Cl) compounds.

Die Metallierung von Bis(diphenylphosphanyl)amin, HN(PPh2)2(4) mit NaH in Gegenwart von N,N,N′,N″,N″‐Pentamethyl‐diethylen‐triamin (PMDTA, 2) führt bei 105 °C in Toluol zum monomerengelben Natrium‐Komplex [(Ph2P)2NNa · PMDTA] (5). Die Kristallstrukturanalyse zeigt, daß die Koordinationssphäre des Natriumions von dem chelatisierenden Triamin 2und [N(PPh2)2]–als N‐ und einzähnigen P‐Donor gebildet wird. Lockere η1‐C‐Kontakte zu 2und [N(PPh2)2]–werden diskutiert. In Gegenwart von [12]‐Krone‐4 reagieren HN(PPh2)2und NaH zu dem dimerengelbgrünen Komplex [{(Ph2P)2NNa}2{[12]‐Krone‐4}5] (6), der in feinen Nadeln kristallisiert. Diese sind aber für eine Kristallstrukturanalyse nicht geeignet. Die dimere, nicht ionische Struktur wurde durch Massenspektroskopie und Leitfähigkeitsmessungen sichergestellt.

Abstract.: The significance of the so-called trigger reaction in the reaction mechanism of the calicheamicin γ1 I anti-cancer drug has been studied with ab initio quantum chemical methods. The structures of four fragments of calicheamicin γ1 I , consisting of either 39 or 41 atoms, have been fully optimized using the Becke-Perdew86 density functional method and the 6-31G* basis sets. The four structures constitute members of an isodesmic reaction for which the reaction energy is a direct measure of the change in activation energy of the Bergman reaction, caused by the structural rearrangements of the preceding trigger reaction. This difference in activation energy has been calculated with density functional theory, using the exchange-correlation functional mentioned above, and with second-order M�ller-Plesset perturbation theory (MP2), employing an ANO-type basis set. In both cases a value of 12 kcal/mol is obtained. The study firmly supports the hypothesis that the significance of the trigger reaction is to saturate a double bond in the vicinity of the enediyne group, which counteracts the formation of the biradical state of the drug. The MP2 computations became feasible by a novel implementation of an integral-direct, distributed-data, parallel MP2 algorithm.

The reaction of Ph2P-N=PPh2-PPh2=N-PPh2(Ph = C6H5, 2) with [CpFe(CO)(μ-CO)]2(Cp = C5H5, 3) yields under elimination of a PPh2-group from 2 and cleavage of the Fe-Fe bond in 3 the monocyclic ferraphosphazene complex Cp(OC)(4) and Ph2P-PPh2(5). In a side reaction the P-P bond of 2 is also cleaved in a redox process to give Cp(OC)(7). Compound 4 has been characterized by a crystal structure determination.

While the reaction of anhydrous iron(III) chloride with the chelate ligand [(C6H5)2P(O)]2NH (6) is an efficient way to synthesize the new tricyclic compound imido-tetraphenyl-diphosphinato-O,O′iron(III), [Fe{O-P(Ph2)=N-P(Ph2)=O}3] (4), treatment of [(C6H5)2P]2NLi (1) with anhydrous iron(III) fluoride in THF represents a simple route to obtain the phosphorus-phosphorus connected species Ph2P-N=PPh2-PPh2=N-PPh2(7). Both compounds were charac­terized by X-ray crystallography, 1H ,31P {1H}, 13C {1H} NMR, IR, Raman and mass spectra.

The metalation of bis(diphenylphosphanyl)amine, HN(PPh2)2(5), with RbOtBu in the presence of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDTA(3)) in toluene surprisingly affords the nearly PMDTAfree RbN(PPh2)2(6a). Recrystallization of 6afrom tetrahydrofuran (THF) yields RbN(PPh2)2ċ0.5 THF(6b). Compounds 6a, bcrystallize in thin needles; however, these are not suitable for X-ray structure analyses. The reactions of 5with MOtBu (M=Rb, Cs) in the presence of 18-crown-6 in toluene yield the monomeric, pale yellow rubidium and caesium complexes [Rb(18-crown-6)(N(PPh2)2)] (7) and [Cs(18-crown-6)(N(PPh2)2)] (8), respectively. Allowing to stand a solution of 8in THFfor three months at 20°C results in a cleavage product of 8. This is identified as the dimeric yellow complex [(Cs(18-crown-6))2(μ-N*P(H)Ph2)2]ċTHF(9). The source of the hydrogen atom in the bridging phosphorane iminate anion [N*P(H)Ph2]−is uncertain. Compounds 7–9are structurally characterized by X-ray analyses. These reveal that [N(PPh2)2]−acts as P-ligating chelate in 7, whereas it coordinates the Cs+as N-donor as well as η2C-donor with one phenyl group in 8. No phosphorus coordination is observed in 8. The two caesium cations in 9are two-fold N-bridged by [N*P(H)Ph2]−. The coordination sphere of each caesium atom is completed by a 18-crown-6 ligand. The solid state 13C NMR spectrum of 8reveals dynamic phenomena (rotation of the 18-crown-6 ligand). In the solid state 31P spectrum of 8, 31P, 31P–J-coupling is observed between the chemically non-equivalent phosphorus sites (J=390 Hz).

The article previews the March 9, 2019 "Nice ’n’ Easy" concert to be performed at the Wiener Konzerthaus theater in Vienna, Austria by the Thomas Quasthoff and a backing jazz trio.

The article reviews several operas including "Trance," composed by Chucho Valdes and Gonzalo Rubalcaba, "Truth is Simple to Consume," composed by Mario Rom's Interzone and "Hope," composed by Kevin Hays and Lionel Loueke performed at the Konzerthaus in Vienna, Austria from March 7-March 20, 2018.

The article previews concert performances at the Wiener Konzerthaus theater in Vienna, Austria including a May 1, 2018 performance by Bill Frisell & Thomas Morgan Duo, a May 4, 2018 performance by John Scofield, and a May 18, 2018 Brad Mehldau Trio concert.

Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4–8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μco-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.