LZA Fizikas un tehnisko zinātņu nodaļas sēde 2014.gada 9.aprīlī


LZA Fizikas un tehnisko zinātņu nodaļas sēde

trešdien, 2014.gada 9.aprīlī plkst. 15.00
LZA Senāta zālē (Rīgā, Akadēmijas laukumā 1, 2.stāvā)

lekcija LZA ārzemju loc. prof. Nila Kristensena (Dānija):

Quantum mechanical calculations of: Electronic, structural, electrical and
optical properties of solids, including pressure and temperature effects.(in English)

LZA ārzemju loc. diploma pasniegšana.

Lūdzam piedalīties!


Quantum mechanical calculations of: Electronic, structural, electrical and optical properties of solids, including pressure and temperature effects.

Niels Egede Christensen http://users?phys.au.dk/nec/

Dept. of Physics and Astronomy, Aarhus University, DK?8000 Aarhus, Denmark.

Equations of state (EOS) for condensed matter link temperature, pressure, density, magnetization and other thermodynamic variables that specify the state of the system considered. Theoretical and experimental studies in general of the EOSs are therefore the most important, and ?if “general” is taken seriously?the only goal of condensed matter physics. Knowing in detail the EOS of a material we also know the elementary interactions, forces, phases and responses of the system to all kinds of external stimuli. Such a complete picture can never be obtained for any system, and the researchers in physics and chemistry must be satisfied with exploring limited sets of possible thermodynamic variables and limited ranges of their values. Temperature, T, and pressure, P, belong to the most important variables used to describe the state. The intensive variable T forms together with the extensive variable S, the entropy, an “energy couple”, and P (intensive) has as its “partner” the extensive variable V, the volume. Microscopic models developed in theoretical condensed matter physics have now reached a level, where it is possible, from parameter?free quantum mechanical calculations, to predict some of the interrelations between the macroscopic state variables. Total energies, forces, vibrational frequencies, magnetic moments, refractive indices etc. can be calculated with a precision that is sufficient for predictions, which are important for the analyses of experimental data, and in “design” of new materials with desired properties.

Some of the computational methods will be described, and results of predicted pressure induced transformations of the alkali metals (like Li and Na), which are “simple” at zero pressure, into “nonsimple” metals, and even into superconductors and insulators at very high compression will be discussed. Some of these high?pressure structures appear to be quite similar to those found for semiconductors, but the bonding is of a very different nature. New artificial structures, mInN/nGaN semiconductor quantum?well superlattices, are designed to have optical properties suited for particular device applications (new light sources). Also thermoelectric applications are briefly discussed, and reasons for the good performance of p?doped PbTe at high temperatures are given.

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