On the Different Characteristics of Medium-Sized van der Waals Molecules Obtainable from ab initio Calculations

Nonempirical ab initio calculations with inclusion of the correlation energy are used to generate, directly or indirectly (via an analytical form of the potential-energy surface), various properties of medium-sized van der Waals molecules. As shown for benzene- • -Ar and the benzene dimer, the calculated characteristics agree with the experimental results. If the experimental values are lacking or if they are uncertain, the theoretical characteristics can be used with confidence

non covalent interactions in anisole co2 n n 1 2 complexes

Non-covalent interactions are a ubiquitous binding motif and a challenge for theory and experiments

Spectroscopy of Isolated Prebiotic Nucleobases

We use multiphoton ionization and double resonance spectroscopy to study the excited state dynamics of biologically relevant molecules as well as prebiotic nucleobases, isolated in the gas phase. Molecules that are biologically relevant to life today tend to exhibit short excited state lifetimes compared to similar but non-biologically relevant analogs. The mechanism is internal conversion, which may help protect the biologically active molecules from UV damage. This process is governed by conical intersections that depend very strongly on molecular structure. Therefore we have studied purines and pyrimidines with systematic variations of structure, including substitutions, tautomeric forms, and cluster structures that represent different base pair binding motifs. These structural variations also include possible alternate base pairs that may shed light on prebiotic chemistry. With this in mind we have begun to probe the ultrafast dynamics of molecules that exhibit very short excited states and search for evidence of internal conversions

S66: A Well-balanced Database of Benchmark Interaction Energies Relevant to Biomolecular Structures

With numerous new quantum chemistry methods being developed in recent years and the promise of even more new methods to be developed in the near future, it is clearly critical that highly accurate, well-balanced, reference data for many different atomic and molecular properties be available for the parametrization and validation of these methods. One area of research that is of particular importance in many areas of chemistry, biology, and material science is the study of noncovalent interactions. Because these interactions are often strongly influenced by correlation effects, it is necessary to use computationally expensive high-order wave function methods to describe them accurately. Here, we present a large new database of interaction energies calculated using an accurate CCSD(T)/CBS scheme. Data are presented for 66 molecular complexes, at their reference equilibrium geometries and at 8 points systematically exploring their dissociation curves; in total, the database contains 594 points: 66 at equilibrium geometries, and 528 in dissociation curves. The data set is designed to cover the most common types of noncovalent interactions in biomolecules, while keeping a balanced representation of dispersion and electrostatic contributions. The data set is therefore well suited for testing and development of methods applicable to bioorganic systems. In addition to the benchmark CCSD(T) results, we also provide decompositions of the interaction energies by means of DFT-SAPT calculations. The data set was used to test several correlated QM methods, including those parametrized specifically for noncovalent interactions. Among these, the SCS-MI-CCSD method outperforms all other tested methods, with a root-mean-square error of 0.08 kcal/mol for the S66 data set

On the Different Characteristics of Medium-Sized van der Waals Molecules Obtainable from ab initio Calculations

Nonempirical ab initio calculations with inclusion of the correlation energy are used to generate, directly or indirectly (via an analytical form of the potential-energy surface), various properties of medium-sized van der Waals molecules. As shown for benzene- • -Ar and the benzene dimer, the calculated characteristics agree with the experimental results. If the experimental values are lacking or if they are uncertain, the theoretical characteristics can be used with confidence

Phusis in Plato

In Plato, the term phusis has a wide range of meanings, so at first sight it doesn't seem that Plato combined with this term a specific philosophical conception. However, the investigation of the Symposium suggests that in the opposition to the Hippocratic conception, in which phusis was conceived of as the nature of human body, Plato conceived of phusis as the human desire or aiming at

From the Socratic Logos to the Parmenidean One: How to read the Euthydemus

The key task of the interpretation the Euthydemus is to establish why Socrates wants to become a pupil of both brothers. It has to do with the "logic" of both brothers' discourse or way of thinking which is, in turn, based on the Parmenidean logic. If we take into account that Socrates is depicted as someone who is not able to arrive at a positive conclusion, then Socrates' motivation for learning from both brothers, i.e., for adopting their wisdom, is to be seen in his effort to overcome the refutational negativity of his own discourse