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This study aims to advance the theoretical understanding of the contextual antecedents underlying abusive supervision. It provides a fresh perspective on how subordinates' perceptions of an abusive supervision climate are shaped in temporary work environments. By developing a robust model, this research examines the relationships between temporary organizational characteristics (i.e., temporariness and membership flexibility), trust in ad-hoc supervisors, and perceived abusive supervision climates. We tested the hypothesized model using data from 340 aircrew engaged in temporary and constantly shifting supervisor–subordinate relationships. The results revealed that: (a) temporariness has a direct negative relationship with trust in ad-hoc supervisors, whereas membership flexibility positively affects this trust; (b) the link between temporariness/membership flexibility and a perceived abusive supervision climate is mediated by trust in ad-hoc supervisors. Furthermore, this study highlights gender interactions in a transactional context, indicating that: (c) females perceive a stronger negative association between trust and abusive supervision climates compared to males; and (d) the relationship between temporariness/membership flexibility and trust in ad-hoc supervisors is significant for women and men, respectively. In conclusion, this study underscores the importance of considering the unique organizational characteristics of temporary work settings when examining abusive supervision. It also emphasizes the role of gender in shaping subordinates' perceptions of a workplace victimization climate, particularly in situations where leader–member exchanges are ephemeral and contractual. [ABSTRACT FROM AUTHOR]

This article explores the contribution of animal-based cultural ecosystem services to tourist well-being within the authentic cultural heritage experience. We assess the construction of tourists' cultural ecosystem services through their cocreation of animal-based experience and its integrative direct links with objective authenticity, existential authenticity, and well-being. The objective is to provide empirical evidence of the cross-category tourist experiences of interactions with animals at cultural heritage sites within the context of those with the cats of the Forbidden City, China. Building on this relationship model, the study further examines and identifies the significant and important parallel mediation effects on the relationship between the cocreation experience and the well-being of the three combinations of (a) attention and objective authenticity, (b) involvement and existential authenticity, and (c) cultural ecosystem service and memorability. Theoretical and managerial implications are provided along with a discussion of research limitations and suggestions for future study. [ABSTRACT FROM AUTHOR]

Carbon-carbon multiply bonded systems are improperly described with standard,wave function-based correlation methods and Gaussian one-particle basis sets implying that thermochemical, spectroscopic, and potential energy surface computations are consistently erroneous. For computations of vibrational modes, the out-of-plane bends can be reported as imaginary at worst or simply too low at best. Utilizing the simplest of aromatic structures (cyclopropenylidene) and various levels of theory, this work diagnoses this known behavior as a combined one-particle and n-particle basis set effect for the first time. In essence, standard carbon basis sets do not describe equally well sp, sp², and sp³ hybridized orbitals, and this effect is exacerbated post-Hartree-Fock by correlation methods. The latter allow for occupation of the π and π* orbitals in the expanded wave function that combine with the hydrogen s orbitals. As a result, the improperly described space is non-physically stabilized by post-Hartree-Fock correlation. This represents a fundamental problem in wavefunction theory for describing carbon. [ABSTRACT FROM AUTHOR]

The Cittàslow philosophy aims to preserve the unique characteristics of places, people, products, food and the environment. Inclusive participation is the focus of the movement for small communities that aim to improve residents' quality of life and share in one of a kind experiences with visitors. Discussion of the Cittàslow movement has been increasing in recent years, and the conceptualization offered in this paper adds to that discourse by showing how the movement, with its unique approach to sustainability and local governance, has the potential to be beneficial to Small Island Developing States (SIDS) by directly and indirectly contributing to sustainable tourism development. Slow Food, Slow Tourism, and sustainability in relation to tourism are discussed to clarify how they all fit into the slow tourism ethos and influence the Cittàslow movement. Interestingly, by examining some of the essentials of the Cittàslow movement, we can ascertain how the quality of life and experience value of tourism complements the Cittàslow approach to sustainable tourism development for SIDS. Sustainability from an island perspective is conceptualized in the context of the Cittàslow model, and the varying elements that are contributors to sustainable tourism development in SIDS are discussed. These include its marketing potential, environmental and agricultural benefits, as well as the definitive socio-economic advances that may come about from implementing such an initiative. Ultimately, our analysis illustrates the SIDS specific impacts that the strategies of the Cittàslow model facilitate, while it also highlights some of the potential barriers to SIDS seamlessly adopting such a concept. [ABSTRACT FROM AUTHOR]

This paper aims to (a) analyze the diverse views held about slow tourism in the Caribbean islands of Antigua and Barbuda, and (b) to propose a conceptual basis for slow tourism as a beneficial component of sustainable development. Using evidence from stakeholder interviews, this paper illustrates how local businesses, products, and the dynamic nature of the tourism industry can be provided with opportunities to propel a regions' sustainability. The results of the study can contribute to the development agendas of many small islands, as they show how to establish effective development policy, management systems, and marketing strategies for sustainable tourism. [ABSTRACT FROM AUTHOR]

A series of high-quality, purely ab initio, quartic force fields (QFFs), computed using a procedure we recently proposed, is reported for NH2- and CCH-. The singles and doubles coupled-cluster method with a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), was used with TZ, QZ, and 5Z quality basis sets and was combined with extrapolation to the one-particle basis-set limit, core-correlation effects, scalar relativistic effects, and higher-order correlation effects to yield accurate QFFs. A “best-guess” reference geometry was determined at the CCSD(T)/5Z level of theory. Analytical transformation removes nonzero gradients to facilitate a second-order perturbation theory spectroscopic analysis. The QFF is transformed into Morse/cosine coordinates in order to perform exact vibrational configuration interaction computations. Equilibrium structures, vibrational frequencies, rotational constants, and selected spectroscopic constants are reported in comparison with experimental values and previous theoretical studies. Higher-order correlation effects are found comparable to core-correlation effects in magnitude, e.g., ∼10 cm-1 for fundamentals, but are of opposite sign. For CCH-, a thorough discussion is presented on effective rotational constants B0. It is concluded that the “best” QFF should incorporate all the small corrections mentioned above. Correspondingly, the best vibrational fundamentals of CCH- are estimated at 502.0 cm-1 (ν2), 1800.9 cm-1 (ν3), and 3204.3 cm-1 (ν1), while the best vibrational fundamentals of NH2- are at 3118.5 cm-1 (ν1), 1447.8 cm-1 (ν2), and 3186.5 cm-1 (ν3). Excellent agreement with high-resolution experiments has been obtained for fundamentals—e.g., 1–3 cm-1 deviation for the symmetric and antisymmetric stretches of NH2-, 3121.93 cm-1 (ν1) and 3190.29 cm-1 (ν3), respectively. Isotopic effects are studied and presented to aid future experimental analyses. The present study should facilitate future characterizations of NH2- and CCH- from astronomical observations or other high-resolution laboratory studies. [ABSTRACT FROM AUTHOR]

In the interstellar medium (ISM) there are many regions where the formation of molecules is kinetically driven rather than thermochemically, which can lead to the formation of many isomers even though some may be fairly higher in energy relative to the molecular global minimum. Recent laboratory experiments where noble gas cations are reacted with pyrimidine favored the formation of C3H3N+, but the molecular structure(s) of this fragment was not determined. Microscopic reversibility means that pyrimidine could form under interstellar conditions should the required C3H3N+ reactant be detected in the ISM. Hence C3H3N+ could be a strong candidate for involvement in the formation of heterocyclic biomolecules such as pyrimidine in the ISM. In this study, we have investigated the low energy isomers of the acrylonitrile ion (C3H3N+) using density functional theory as well as high levels of ab initio theory, namely, the singles and doubles coupled-cluster theory that includes a perturbational correction for connected triple excitations, denoted as CCSD(T). An automated stochastic search procedure, Kick, has been employed to find isomers on the ground state doublet potential energy surface. Several new structures, along with all the previously reported minima, have been found. The global minimum H2CCCNH+ is energetically much lower than either H2CC(H)CN+, the acrylonitrile ion, or HCC(H)NCH+, the most likely intermediate of the reaction between HCCH+ and HCN. These isomers are connected to the global minimum via several transition states and intermediates. The results indicate that not only the global minimum but also several higher energy isomers of the C3H3N+ ion could be important in interstellar pyrimidine formation. The isomeric molecules have the necessary CCNC backbone needed for the reaction with HCN to form the cyclic pyrimidine framework. The structural and rotational parameters of all the isomers studied in this work have been predicted at the CCSD(T) level of theory with the anticipation that it will expedite their laboratory as well as astronomical identification. [ABSTRACT FROM AUTHOR]

A procedure for the calculation of molecular quartic force fields (QFFs) is proposed and investigated. The goal is to generate highly accurate ab initio QFFs that include many of the so-called “small” effects that are necessary to achieve high accuracy. The small effects investigated in the present study include correlation of the core electrons (core correlation), extrapolation to the one-particle basis set limit, correction for scalar relativistic contributions, correction for higher-order correlation effects, and inclusion of diffuse functions in the one-particle basis set. The procedure is flexible enough to allow for some effects to be computed directly, while others may be added as corrections. A single grid of points is used and is centered about an initial reference geometry that is designed to be as close as possible to the final ab initio equilibrium structure (with all effects included). It is shown that the least-squares fit of the QFF is not compromised by the added corrections, and the balance between elimination of contamination from higher-order force constants while retaining energy differences large enough to yield meaningful quartic force constants is essentially unchanged from the standard procedures we have used for many years. The initial QFF determined from the least-squares fit is transformed to the exact minimum in order to eliminate gradient terms and allow for the use of second-order perturbation theory for evaluation of spectroscopic constants. It is shown that this step has essentially no effect on the quality of the QFF largely because the initial reference structure is, by design, very close to the final ab initio equilibrium structure. The procedure is used to compute an accurate, purely ab initio QFF for the H2O molecule, which is used as a benchmark test case. The procedure is then applied to the ground and first excited electronic states of the HO2+ molecular cation. Fundamental vibrational frequencies and spectroscopic constants from these highly accurate QFFs are compared and contrasted with previous experiment and theory. It is concluded that the spectroscopic constants determined for the X3A″ and A1A′ states of HO2+ are the most accurately available. [ABSTRACT FROM AUTHOR]

Danionella cerebrum (DC) is a promising vertebrate animal model for systems neuroscience due to its small adult brain volume and inherent optical transparency, but the scope of their cognitive abilities remains an area of active research. In this work, we established a behavioral paradigm to study visual spatial navigation in DC and investigate their navigational capabilities and strategies. We initially observed that adult DC exhibit strong negative phototaxis in groups but less so as individuals. Using their dark preference as a motivator, we designed a spatial navigation task inspired by the Morris water maze. Through a series of environmental cue manipulations, we found that DC utilize visual cues to anticipate a reward location and found evidence for landmark-based navigational strategies wherein DC could use both proximal and distal visual cues. When subsets of proximal visual cues were occluded, DC were capable of using distant contextual visual information to solve the task, providing evidence for allocentric spatial navigation. Without proximal visual cues, DC tended to seek out a direct line of sight with at least one distal visual cue while maintaining a positional bias toward the reward location. In total, our behavioral results suggest that DC can be used to study the neural mechanisms underlying spatial navigation with cellular resolution imaging across an adult vertebrate brain. • Adult Danionella cerebrum (DC) exhibit strong negative phototaxis • DC are capable of learning a Morris water maze-like spatial navigation task • DC use environmental visual cues to solve the spatial navigation task • Performance in this task is modulated by the visual environmental context The translucent fish Danionella cerebrum (DC) are a promising systems neuroscience animal model. Lee and Briggman show that adult DC exhibit negative phototaxis and apply this as a motivator in a Morris water maze-like spatial navigation task. DC use visual cues to learn this task; their performance is modulated by the environmental visual context. [ABSTRACT FROM AUTHOR]

Reports on the time-dependent density functional theory (TDDFT) study on the electronic excitation energies of polycyclic aromatic hydrocarbon radical cations of naphthalene, anthracene, pyrene and perylene. Use of the Tamm-Dancoff approximation to TDDFT to calculate the electronic excitation energies and oscillator strengths.

This study examines the influence of social support from intermediary organizations on innovativeness and subjective happiness in community-based tourism (CBT). The authors collected data from 236 residents who had participated in the Tour Dure project in South Korea. The analysis, using partial least square structural equation modeling (PLS-SEM), shows that social support from intermediary organizations has a positive effect on the innovativeness of residents. Further, the more innovativeness the residents showed, the more their subjective happiness increased. In other words, social support from intermediary organizations plays an important role in improving innovativeness, and in turn, the subjective happiness of residents. There have been many claims that resident participation is important in CBT, but it has usually been treated as a slogan without offering specific proposals for boosting such participation. This study discovered that the social support given by intermediary organizations to residents plays an important role in innovativeness and subjective happiness. It also shows that it is effective to encourage residents' participation in CBT by offering social support from intermediary organizations. [ABSTRACT FROM AUTHOR]

To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt 'Best Theory + Reliable High-resolution Experiment' (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The 'Ames-1' potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σrms = 0.02–0.03 cm-1 for five isotopologues. The 'Ames-1' dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (SAmes) are demonstrated through comparisons with HITRAN (SHITRAN), NOSL-296 (SNOSL), recent observed intensities (Sobs) and Effective Dipole Model (EDM) intensities (SEDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for SAmes. The SAmes provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at and https://doi.org/10.48667/9kmk-0334. [ABSTRACT FROM AUTHOR]

Accurate binding energies of molecules to water clusters are relevant for understanding intermolecular interactions and various chemical applications. They enter models of interstellar chemical processes, as binding to icy grains influences surface reactions and thus affects calculated gas-phase abundances. Unfortunately, many astrochemical molecules (especially radicals and ions) are incompletely characterised in these models. To address this, we report computational searches for optimal structures and benchmark binding and condensation energies for sets of neutral, radical, cationic, and anionic molecules of astrochemical relevance with clusters of $ N=1{\rm -}4 $ N = 1 − 4 water molecules. These calculations utilised reliable density functionals for geometry optimisation, and coupled cluster (CCSD(T)) single point calculations with large basis sets. Four energetic binding motifs (weak, intermediate, strong or covalently bonded) were observed depending on the chemical nature of the guest molecule. Neutral closed and open-shell molecules with strong dipoles and a greater potential for hydrogen bonding are more tightly bound to water clusters compared to non-polar ones. For closed-shell cationic and anionic species, barrier-less reactions with water clusters occur, which reveals radical-free routes to molecular processing in the gas phase and on amorphous ice surfaces. [ABSTRACT FROM AUTHOR]

Highlights • Spectroscopic data for the remote sensing of :CNH 2 + and :CCH 2 in Titans atmosphere are provided. • :CNH 2 + has the same m/z = 28 value as the HCNH + ion believed to have been sampled by Cassinis INMS. • :CNH 2 + has a large (2.2 D) dipole moment and a bright infrared feature at 5.8 µm. Abstract The highest peak in Cassini 's INMS data for stratospheric flybys of Titan's atmosphere is m / z = 28. While this has mostly been attributed to HCNH + , minor contributions from N 2 + and C 2 H 2 + are also likely. However, this work shows that :CNH 2 + may also be present in a kinetically-favorable potential well based on high-level quantum chemical computations. The ionization energy of N 2 is much higher than the isomerization barrier between HCNH + and :CNH 2 +. As such, we present computations that provide vibrational and rotational spectroscopic data for the possible remote sensing of this molecule in Titan's atmosphere. Such data are also computed for the isoelectronic :CCH 2 molecule, and comparison to previous laboratory experiments and quantum chemical computations, where available for the hydrocarbon, is excellent. Consequently, the data provided in this work should allow for initial searches for :CNH 2 + as well as refinements of data for :CCH 2 both in the laboratory and even in Titan's atmosphere. [ABSTRACT FROM AUTHOR]

Hypothesis The manipulation of nanosheets on a fluid-fluid interface remains a significant challenge. At this interface, hydrodynamic forces can be used for long-range transport (>1× capillary length) but are difficult to utilize for accurate and repeatable positioning. While capillary multipole interactions have been used for particle trapping, how these interactions manifest on large but thin objects, i.e., nanosheets, remains an open question. Hence, we posit hydrodynamic forces in conjunction with capillary multipole interactions can be used for nanosheet transport and trapping. Experiments We designed and characterized a fluidic device for transporting and trapping nanosheets on the water-air interface. Analytical models were compared against optical measurements of the nanosheet behavior to investigate capillary multipole interactions. Energy-based modeling and dimensional analysis were used to study trapping stability. Findings Hydrodynamic forces and capillary interactions successfully transported and trapped nanosheets at a designated trapping location with a repeatability of 10% of the nanosheet’s length and 12% of its width (length = 1500 µm, width = 1000 µm) and an accuracy of 20% of their length and width. Additionally, this is the first report that surface tension forces acting upon nanoscale-thick objects manifest as capillary quadrupolar interactions and can be used for precision manipulation of nanosheets. [ABSTRACT FROM AUTHOR]

The formalism for a relativistic open-shell CCSD(T) method is presented and implemented in a computer program, RELCCSD. The code can be used for calculations with 2- or 4-component relativistic reference wave functions and allows a full inclusion of the spin–orbit coupling. The code is interfaced to the MOLFDIR program system. We illustrate its use with ab initio calculations of the fine structure splittings of Cl, FO, ClO, O+2, and O-2. The triples correction is found to make a large contribution to the Cl atom splitting, which is within 23 cm-1, of the experimental value. The molecular results are within 4 cm-1 of the experimental values where these are available. The value for FO is predicted to be -195±4 cm-1, in good agreement with experiment. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The quartic force field of ethylene, C2H4, has been calculated ab initio using augmented coupled cluster, CCSD(T), methods and correlation consistent basis sets of spdf quality. For the 12C isotopomers C2H4, C2H3D, H2CCD2, cis-C2H2D2, trans-C2H2D2, C2HD3, and C2D4, all fundamentals are reproduced to better than 10 cm-1, except for three cases where the error is 11 cm-1. Our calculated harmonic frequencies suggest a thorough revision of the accepted experimentally derived values. Our computed and empirically corrected re geometry differs substantially from experimentally derived values: Both the predicted rz geometry and the ground-state rotational constants are, however, in excellent agreement with experiment, suggesting revision of the older values. Anharmonicity constants agree well with experiment for stretches, but differ substantially for stretch–bend interaction constants, due to equality constraints in the experimental analysis that do not hold. Improved criteria for detecting Fermi and Coriolis resonances are proposed and found to work well, contrary to the established method based on harmonic frequency differences that fails to detect several important resonances for C2H4 and its isotopomers. Surprisingly good results are obtained with a small spd basis at the CCSD(T) level. The well-documented strong basis set effect on the ν8 out-of-plane motion is present to a much lesser extent when correlation-optimized polarization functions are used. Complete sets of anharmonic, rovibrational coupling, and centrifugal distortion constants for the isotopomers are available as supplementary material to the paper via the World-Wide Web. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A very accurate ab initio quartic force field for CH4 and its isotopomers is presented. The quartic force field was determined with the singles and doubles coupled-cluster procedure that includes a quasiperturbative estimate of the effects of connected triple excitations, CCSD(T), using the correlation consistent polarized valence triple zeta, cc-pVTZ, basis set. Improved quadratic force constants were evaluated with the correlation consistent polarized valence quadruple zeta, cc-pVQZ, basis set. Fundamental vibrational frequencies are determined using second-order perturbation theory anharmonic analyses. All fundamentals of CH4 and isotopomers for which accurate experimental values exist and for which there is not a large Fermi resonance, are predicted to within ±6 cm-1. It is thus concluded that our predictions for the harmonic frequencies and the anharmonic constants are the most accurate estimates available. It is also shown that using cubic and quartic force constants determined with the correlation consistent polarized double zeta, cc-pVDZ, basis set in conjunction with the cc-pVQZ quadratic force constants and equilibrium geometry leads to accurate predictions for the fundamental vibrational frequencies of methane, suggesting that this approach may be a viable alternative for larger molecules. Using CCSD(T), core correlation is found to reduce the CH4 re by 0.0015 Å. Our best estimate for re is 1.0862±0.0005 Å. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An accurate ab initio quartic force field for HNO has been determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T), in conjunction with the correlation consistent polarized valence triple zeta (cc-pVTZ) basis set. Improved harmonic frequencies were determined with the cc-pVQZ basis set. Fundamental vibrational frequencies were determined using a second-order perturbation theory analysis and also using variational calculations. The N–O stretch and bending fundamentals are determined well from both vibrational analyses. The H–N stretch, however, is shown to have an unusually large anharmonic correction, and is not well determined using second-order perturbation theory. The H–N fundamental is well determined from the variational calculations, demonstrating the quality of the ab initio quartic force field. The zero-point energy of HNO that should be used in isodesmic reactions is also discussed. [ABSTRACT FROM AUTHOR]

By representing orbital products in an expansion basis, certain classes of two-electron integrals are approximated for use in CCSD(T) calculations (singles and doubles coupled-cluster plus a perturbational estimate of the effects of connected triple excitations). This leads to a very large reduction in disk storage and input/output requirements, with usually only a modest increase in computational effort. The new procedure will allow very large CCSD(T) calculations to be undertaken, limited only by available processor time. Using the molecular basis as the expansion basis, explicit numerical comparisons of equilibrium geometries, harmonic frequencies, and energy differences indicate that the error due to the use of approximate integrals is less than the error associated with truncation of the molecular basis set. [ABSTRACT FROM AUTHOR]

A comparative study is presented of the various recently developed open-shell perturbation theories that are based on a restricted Hartree–Fock reference wave function. Included in this study are issues concerning spin contamination, implementational considerations, and numerical comparisons at the second-order of perturbation theory for equilibrium geometries, vibrational frequencies, and singlet–triplet energy differences. Based on all of these considerations, it is concluded that the z-averaged perturbation theory (ZAPT) method is to be preferred over the other recently devised spin–orbital perturbation theories, while the spin-free OPT2 method possesses some advantages and disadvantages relative to the ZAPT method. In particular, it is shown that OPT2 energies are not invariant to rotations among singly-occupied degenerate molecular orbitals. [ABSTRACT FROM AUTHOR]

Singles and doubles coupled-cluster (CCSD) theory and the CCSD(T) method, CCSD plus a perturbational estimate of the effects of connected triple excitations, have been used to determine the equilibrium structures, dipole moment, vibrational frequencies, and infrared intensities of the HNO, FNO, and ClNO species. A double polarized triple-zeta (TZ2P) quality basis set was used. The CCSD(T) results are found to be in very good agreement with experiment, indicating that the CCSD(T) method performs well in describing the weak X–NO single bond. The experimental heats of formation of the FNO, and ClNO species are examined for internal consistency with experimental data for FNO2 and ClNO2, by using an isodesmic reaction. It is concluded that the experimental data exhibit a small inconsistency. An approach, involving in addition the use of homodesmic reactions, by which a more consistent set of thermochemical data may be obtained is proposed and discussed. [ABSTRACT FROM AUTHOR]

An efficient formulation of our recently proposed [Chem. Phys. Lett. 199, 211 (1992)] open-shell singles and doubles coupled-cluster (OCCSD) method is presented. This formulation is in terms of spatial orbital one- and two-electron integrals. Our new OCCSD method is based on ‘‘symmetric spin orbitals’’ and is thus symmetric (or antisymmetric) in the spin indices. It therefore contains about half the number of independent parameters in the coupled-cluster wave function compared to other open-shell CCSD methods. It is shown that the formulation presented here contains less than half the number of n6 steps (where n is the number of molecular orbitals) of other recently proposed open-shell CCSD methods. A new approach by which amplitudes in our method may be compared with amplitudes in a previous OCCSD method is examined. [ABSTRACT FROM AUTHOR]

The protonation of N2O and the intramolecular proton transfer in N2OH+ have been studied using large basis sets in conjunction with second-order many-body perturbation theory (MP2), singles and doubles coupled cluster (CCSD), the augmented coupled cluster method [CCSD(T)], and complete active space self-consistent field (CASSCF) methods. It is shown that MP2 is inadequate even for HNNO+, which has a minor nondynamical correlation effect; for the transition state only CCSD(T) produces a reliable geometry due to serious nondynamical correlation effects. Harmonic frequencies accurate to 50 cm-1 or better are predicted for both protonated species. The proton affinity at 298.15 K is found to be 137.6 kcal/mol, in excellent agreement with the recent experimental redetermination of 137.3±1 kcal/mol; the HNNO+ isomer is found to be 4.4 kcal/mol above the HONN+ isomer, with an interconversion barrier of ∼89 kcal/mol, herewith confirming recent experimental evidence that both species occur together with an energy difference of 6±1.5 kcal/mol. Comparison of the traditional double-zeta plus polarization (DZP) basis and the newer correlation consistent polarized valence double zeta (cc-pVDZ) basis set appears to indicate that the latter might lead to more accurate geometries and harmonic frequencies, although a more detailed investigation would be needed before any definitive conclusions. [ABSTRACT FROM AUTHOR]

The quartic force field of ammonia is computed using basis sets of spdf/spd and spdfg/spdf quality and an augmented coupled cluster method. After correcting for Fermi resonance, the computed fundamentals and ν4 overtones agree on average to better than 3 cm-1 with the experimental ones except for ν2. The discrepancy for ν2 is principally due to higher-order anharmonicity effects. The computed ω1, ω3, and ω4 confirm the recent experimental determination by Lehmann and Coy but are associated with smaller error bars. The discrepancy between the computed and experimental ω2 is far outside the expected error range, which is also attributed to higher-order anharmonicity effects not accounted for in the experimental determination. Spectroscopic constants are predicted for a number of symmetric and asymmetric top isotopomers of NH3. [ABSTRACT FROM AUTHOR]

The lowest 1Σ+ and 3Π states of the BN molecule have been studied using multireference configuration interaction (MRCI) and averaged coupled-pair functional (ACPF) methods and large atomic natural orbital (ANO) basis sets, as well as several coupled cluster methods. Our best calculations strongly support a 3Π ground state, but the a 1Σ+ state lies only 381±100 cm-1 higher. The a 1Σ+ state wave function exhibits strong multireference character and, consequently, the predictions of the perturbationally-based single-reference CCSD(T) coupled cluster method are not as reliable in this case as the multireference results. The best theoretical predictions for the spectroscopic constants of BN are in good agreement with experiment for the X 3Π state, but strongly suggest a misassignment of the fundamental vibrational frequency for the a 1Σ+ state. [ABSTRACT FROM AUTHOR]

The three lowest-lying isomers of Cl2O2 have been investigated using state-of-the-art ab initio quantum-mechanical methods. Electron correlation methods that have been used include second-order Mo\ller–Plesset perturbation theory, singles and doubles coupled-cluster (CCSD) theory, and the CCSD(T) method, which incorporates a perturbational estimate of the effects of connected triple excitations. Accurate relative energies have been obtained using the CCSD(T) method in conjunction with large atomic natural orbital basis sets that include up to g-type functions. Our best estimate is that the ClClO2 and ClOClO isomers lie 0.9±2.0 and 10.1±4.0 kcal/mol higher in energy (0 K), respectively, than the more stable ClOOCl peroxide form. In order to obtain accurate equilibrium geometries it is necessary to include f-type functions in the one-particle basis set. The vibrational spectra (including IR intensities) of all three isomers are computed and compared with experimental data for ClOOCl and ClClO2. The theoretical and experimental vibrational frequencies agree very well except for the symmetric combination of Cl–O stretches in ClOOCl, where it is concluded that the experimental band is most likely due to the antisymmetric Cl–O stretch. The heat of formation of ClOOCl is computed using an isodesmic reaction involving Cl2O, H2O, and HOOH, and determined to be 34.2 kcal/mol (0 K). The largest uncertainty in this value is due to potential errors in the experimental heat of formation of Cl2O. Using the experimental heat of formation of ClO, the dissociation energy of ClOOCl relative to 2 ClO is computed to be 14.9 kcal/mol at 298 K. The equilibrium structures and vibrational spectra of Cl2O, H2O, and HOOH from our highest-level calculations are found to be in excellent agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The equilibrium structures, vibrational spectra, and relative energetics of the FNO2, cis-FONO, and trans-FONO isomers have been investigated using high-levels of ab initio theory. These methods include second-order Mo\ller–Plesset perturbation theory (MP2), singles and doubles coupled-cluster (CCSD) theory, and the CCSD(T) method, which incorporates a perturbational estimate of the effects of connected triple excitations. FNO2 is determined to be 36.9±2.5 kcal/mol (0 K) more stable than cis-FONO, which is more stable than trans-FONO by 2.5±1.0 kcal/mol (0 K). The molecular structure of cis-FONO is shown to have typical F–O and central O–N single bond distances, indicating that cis-FONO has a structure analogous to HONO. The computed vibrational spectrum of cis-FONO is shown to be consistent with infrared matrix isolation experiments, including isotopic shifts. The experimentally deduced structure of FONO (based on a normal coordinate analysis), however, is shown to be incorrect because one of the vibrational bands included in the normal coordinate analysis is either a combination band or an overtone. [ABSTRACT FROM AUTHOR]

The equilibrium structures, dipole moments, harmonic vibrational frequencies, and infrared intensities of NH3, FON, Be3, BeC2, and BeO2 have been determined using the coupled-cluster and Brueckner electron correlation methods. The singles and doubles coupled-cluster (CCSD) and the Brueckner doubles (BD) methods have been employed and the corresponding methods that include a perturbational estimate of connected triple excitations [i.e., CCSD(T) and BD(T)] have also been investigated. The T1 diagnostic [Int. J. Quantum Chem. Symp. 23, 199 (1989)] is found to provide a good indication of the magnitude of the difference between the results obtained with the coupled-cluster and Brueckner methods. For NH3, the T1 diagnostic is small and so the differences between results obtained from coupled-cluster and Brueckner theories are quite small. For the other four molecules the T1 diagnostic is larger, and so the differences between the coupled-cluster and Brueckner methods become larger. However, it is found for all of the molecules considered in this study that inclusion of the contribution from connected triple excitations is more important than the differences between the Brueckner and coupled-cluster correlation methods. [ABSTRACT FROM AUTHOR]

The analytic energy gradient for the single and double excitation coupled-cluster (CCSD) wave function has been reformulated and implemented in a new set of programs. The reformulated set of gradient equations have a smaller computational cost than any previously published. The iterative solution of the linear equations and the construction of the effective density matrices are fully vectorized, being based on matrix multiplications. The new method has been used to investigate the Cl2O2 molecule, which has recently been postulated as an important intermediate in the destruction of ozone in the stratosphere. In addition to reporting computational timings, the CCSD equilibrium geometries, harmonic vibrational frequencies, infrared intensities, and relative energetics of three isomers of Cl2O2 are presented. The relative energies of the three isomers are further investigated using large atomic natural orbital basis sets in conjunction with the CCSD(T) method, which includes a perturbational estimate of connected triple excitations. The peroxide form of Cl2O2 is predicted to be the lowest energy isomer with the ClClO2 form lying 5.1±3.5 kcal/mol higher in energy. [ABSTRACT FROM AUTHOR]

An efficient formulation of the analytic energy gradient for the single and double excitation coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), is presented. The formulation presented here has a smaller computational cost than any previous formulation, and the algebraic manipulations that lead to the additional savings may be applied generally to the analytic gradient of Mo\ller–Plesset perturbation theory energies. The energy contribution from connected triple excitations scales as n3on4v+n4on3v, and the additional work needed for the gradient scales as 2n3on4v+2n4[ATOTHER]@[/ATOTHER]in3v, where no is the number of doubly occupied orbitals and nv is the number of unoccupied orbitals. The new formulation has been implemented in an efficient set of programs that utilize highly vectorized algorithms and has been used to investigate the equilibrium structures, harmonic vibrational frequencies, infrared intensities, and energy separation of cis- and trans-HONO. [ABSTRACT FROM AUTHOR]

The tetrahedral (Td) form of the N4 molecule has been investigated via ab initio quantum mechanical methods. The lowest triplet state of N4 in the tetrahedral region of the potential energy surface, and the barrier separating TdN4 from two N2 molecules have also been examined. Both the transition state and 3A‘ state have Cs symmetry. The singlet state of tetrahedral N4 is predicted to lie 13 kcal/mol below the 3A‘ state. The energy difference between TdN4 and two N2 molecules is accurately determined to be 186 kcal/mol while the barrier separating these species is found to be about 61 kcal/mol. The possibility that TdN4 may be used as a high energy density fuel is investigated and discussed. In addition, a highly accurate determination of the equilibrium structure, harmonic vibrational frequencies, and infrared intensities of TdN4 has been performed using large atomic natural orbital (ANO) basis sets in conjunction with the coupled-cluster single and double (CCSD) excitation level of theory and the CCSD(T) extension. The largest ANO basis sets used for N4 contain f-type functions. Analogous studies of the N2 molecule are presented in order to judge the reliability of the theoretical predictions for the experimentally unknown TdN4. [ABSTRACT FROM AUTHOR]

The equilibrium geometries, binding energies, and harmonic frequencies of Mg3 and Mg4 have been determined using large atomic natural orbital basis sets in conjunction with high levels of electron correlation. The correlation treatments comprise multireference configuration interaction (MRCI), singles and doubles coupled-cluster (CCSD) theory and the CCSD(T) extension that includes a perturbational estimate of connected triple excitations. As with our previous studies of small Be clusters, the CCSD(T) method is found to reproduce the MRCI results with a remarkable degree of accuracy and at a fraction of the computational cost. Using the CCSD(T) method, full quartic force fields for Mg3 and Mg4 have been determined and anharmonic analyses have been performed using second-order perturbation theory. Vibration–rotation interaction constants and centrifugal distortion constants have also been determined. The fundamental vibrational frequencies are predicted to occur at ν1 (a’1)=96 and ν2 (e’)=104 cm-1 for Mg3, and ν1 (a1)=184, ν2 (e)=143, and ν3 (t2)=167 cm-1 for Mg4. Infrared (IR) intensities, evaluated for the IR active modes via the double harmonic approximation, are 0.2 and 2.4 km/mol for the e’ (Mg3) and t2 (Mg4) modes, respectively. [ABSTRACT FROM AUTHOR]

Electron correlation energies have been determined for 14 different molecules which represent a range of chemical bonding situations. These have been determined with the coupled-cluster single, double, and triple (CCSDT) excitation model as well as with several coupled-cluster methods that include only an approximate treatment of connected triple excitations, viz. CCSDT-1a, CCSDT-1b, CCSDT-2, CCSDT-3, CCSDT-4, and the recently proposed CCSD(T) method. All of the CCSDT-x methods include the effects of connected triple excitations in an iterative manner, whereas in CCSDT(T) these are included perturbationally. For chemical systems which are well represented by a single-determinant reference function, some of the CCSDT-xmethods (CCSDT-1a, CCSDT-1b, and CCSDT-4) perform marginally better than the CCSD(T) approach in reproducing the CCSDT results. However, as nondynamical correlation becomes more important the good agreement from the CCSDT-x methods deteriorates rapidly, while the error in CCSD(T) remains more consistent. For the 14 molecules considered in this work, the average error of the CCSD(T) method relative to CCSDT (667 μhartrees) is considerably below that obtained from any of the CCSDT-x methods. It is concluded that CCSD(T) is to be preferred over any of the other approximate methods, both because it is the least expensive and also because it is generally the most accurate approximation to CCSDT. [ABSTRACT FROM AUTHOR]