| 1. |
- Blunden, Jessica, et al.
(författare)
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State of the Climate in 2012
- 2013
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 94:8, s. S1-S258
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Tidskriftsartikel (refereegranskat)abstract
- For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
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| 2. |
- Linares, Mathieu, et al.
(författare)
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Complex Polarization Propagator Approach in the Restricted Open-Shell, Self-Consistent Field Approximation: The Near K-Edge X-ray Absorption Fine Structure Spectra of Allyl and Copper Phthalocyanine
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115:18, s. 5096-5102
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Tidskriftsartikel (refereegranskat)abstract
- A presentation of the complex polarization propagator in the restricted open-shell self-consistent field approximation is given. It rests on a formulation of a resonant-convergent, first-order polarization propagator approach that makes it possible to directly calculate the X-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted X-ray spectra relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects. The method is applied to the calculation of the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine. Comparison is made between the spectra of the radicals and those of the corresponding cations and anions to assess the effect of the increase of electron charge in the frontier orbital. The method offers the possibility for unique assign-lent of symmetry-independent atoms. The overall excellent spectral agreement motivates the application of the method as a routine precise tool for analyzing X-ray absorption of large systems of technological interest.
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| 3. |
- List, N. H., et al.
(författare)
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Rotationally averaged linear absorption spectra beyond the electric-dipole approximation
- 2017
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Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 115, s. 63-74
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Tidskriftsartikel (refereegranskat)abstract
- Based on the recently developed implementation of the full semi-classical field–matter interaction operator, we present a numerically accurate yet efficient scheme to perform rotational averaging of linear absorption spectra beyond the electric-dipole approximation. This allows for a gauge-origin independent determination of UV/vis and X-ray absorption spectra for randomly oriented systems such as multilayers, liquids, and gas phase samples. The approach is illustrated by the determination of spectral intensities of electric-dipole allowed π → π* transitions and electric-dipole forbidden n → π* transitions in the UV–vis region of the spectrum as well as electric-dipole forbidden 1s → 3d transitions in the X-ray region of the spectrum. The employed Lebedev quadrature scheme shows very fast convergence with respect to the number of symmetry-independent quadrature points – in all considered cases, the oscillator strengths for the randomly oriented systems are fully converged with use of only seven quadrature points.
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| 4. |
- Niskanen, Johannes, et al.
(författare)
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Relativistic contributions to single and double core electron ionization energies of noble gases
- 2011
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 135:5, s. 054310-
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Tidskriftsartikel (refereegranskat)abstract
- We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac-Coulomb Hamiltonian is found to predict a scaling ratio of similar to 4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.
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| 5. |
- Norman, Patrick, 1968-, et al.
(författare)
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Microscopic theory of nonlinear optics
- 2006
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Ingår i: Nonlinear optical properties of matter: From molecules to condensed phases. - Dordrecht : Springer. - 9781402048500 - 9781402048494 ; , s. -694
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Non-Linear Optical Properties of Matter: From Molecules to Condensed Phases attempts to draw together both theory and application in this field. As such it will be of interest to both experimentalists and theoreticians alike. Divided into two parts, Part 1 is concerned with the theory and computing of non-linear optical (NLO) properties while Part 2 reviews the latest developments in experimentation.Part 1: Surveys the current advances in the computation of the NLO properties of molecules, crystalline solids and nano-particles. It examines the methods employed to compute the properties of both microscopic and macroscopic forms of matter.Part 2: Covers the recent advances on the NLO properties of organometallic compounds, rotaxanes, glasses, Langmuir-Blodget films, gold and silver nano-particles etc. Strategies to develop novel NLO materials are also discussed along with the Hyper-Rayleigh scattering technique.This book will be invaluable to researchers and students in academia and industry. It will be of particular interest to anyone involved in materials science, theoretical and computational chemistry, chemical physics, and molecular physics.
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| 6. |
- Norman, Patrick, 1968-
(författare)
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Nonlinear Optical Properties of Fullerenes, Oligomers, and Solutions
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents development and applications of modern tools in ab initio quantum chemistry for obtaining linear and nonlinear response properties of molecules in the gas phase and in solution. The external perturbing fields are primarily electric in nature with frequencies in the optical region.The framework for this achievement is denoted response theory, a formulation of time-dependent perturbation theory, which has been extended to include fourth-order properties fully analytically for self-consistent field (SCF) and multi-configurational SCF (MCSCF) reference states. This extension refers both to the vacuum theory as well as to a self-consistent reaction field model for properties in solution.Applications are presented, displaying both the possibilities and limitations of the theory. Highly electron correlated MCSCF reference states are used for small molecules both in the gas phase and in solution to obtain accurate values of ground and excited state polarizabilities $\alpha$, and ground state hyperpolarizabilities $\beta$ and $\gamma$. Excited state properties are addressed without explicit optimization of the state in question but instead by computing a double residue of the cubic response function. We have in some cases considered both the electronic and the vibrational contributions to these properties. Another direction that has been pursued is to, at the random phase approximation (RPA) level, extend the range of applications for large-scale systems by means of direct atomic orbital driven routines in a parallel scheme. In this context, we address structure-to-property relations for two-dimensional hydrocarbon oligomers, and electron-delocalization of fullerenes. With small we mean molecules with up to 15 atoms and with large-scale we mean molecules with up to 150 atoms.
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| 7. |
- Nörby, Morten, et al.
(författare)
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Assessing frequency-dependent site polarisabilities in linear response polarisable embedding
- 2017
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Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 115, s. 39-47
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we discuss the impact of using a frequency-dependent embedding potential in quantum chemical embedding calculations of response properties. We show that the introduction of a frequency-dependent embedding potential leads to further model complications upon solving the central equations defining specific molecular properties. On the other hand, we also show from a numerical point of view that the consequences of using such a frequency-dependent embedding potential is almost negligible. Thus, for the kind of systems and processes studied in this paper the general recommendation is to use frequency-independent embedding potentials since this leads to less complicated model issues. However, larger effects are expected if the absorption bands of the environment are closer to that of the region treated using quantum mechanics.
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