1,720,973 research outputs found
Free energies of molecular crystal surfaces by computer simulations: application to tetrathiophene
No full textMolecular modeling of crystalline oligothiophenes: testing and development of improved force fields
No full textSimulation of the surface properties of molecular crystals
No full textThe surface structure of molecular crystals is of interest for several applications, such as the crystallization of pharmaceutical compounds or the properties of thin films for organic electronics. Unlike inorganic solids, such as ionic or semiconductor crystals, molecular solids generally show no reconstructions and little relaxation at the surface. However, molecular motions at the surface and within the bulk of the crystals may be significantly different in this case. Computer simulation by Molecular Dynamics (MD) is a useful complement to experimental investigations by methods such as AFM (Atomic Force Microscopy), which can hardly detect these effects. Our group has applied it to the investigation of molecular crystal surfaces. We have also implemented a method for the calculation of surface free energies, which are not readily measured experimentally. The method, which employs the technique of "thermodynamic integration", requires significant computer resources
Modeling of molecular packing and conformation in oligofluorenes
No full textWe describe the application of molecular modeling to study problems related to the packing and conformation of oligofluorene molecules in the solid state. First of all, we describe an improved force field for oligofluorenes. The model is based on the MM3 force field for the intramolecular degrees of freedom, but it relies oil A initio calculations for the torsion potential between two monomers and the electrostatic interactions. We also report ab initio calculations of the interaction potentials between fluorene and fluorenone units. The force field has been tested on the crystal structures of a fluorene monomer, a dimer, and a pentamer containing a fluorenone at the center. It has then been employed to Study conformational defects of the chains, both ill vacuo and in the bulk. We find that certain modes of inversion from right-handed to left-handed helices are also possible within the constraining environment of the crystals. The effect of the presence of two different types of side chains has been also addressed. Finally, the possibility of having two fluorene units parallel and close to each other has been investigated as a model of a ground-state precursor of an excimer. Our Simulations show that this configuration is sterically and energetically unfavorable so that formation of all excimer following optical excitation appears to be unlikely
Incommensurate epitaxy of tetrathiophene on potassium hydrogen phthalate: insights from molecular simulation
No full textSulla struttura locale di alcuni liquidi ionici modello: approccio integrato NMR e dinamica molecolare
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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