Kostya Trachenko

<[email protected]>

Kostya Trachenko: Reader in Physics, Queen Mary University of London.

Before joining QMUL, I was a PhD student and an EPSRC Advanced Research Fellow in Cambridge.

My research interests mostly lie in theoretical and computational condensed matter physics: fundamental theory of liquid and supercritical states of matter, glass transition, glasses, high pressure and radiation damage effects including in nuclear waste forms and fusion reactors. I am also interested in links between field theory and condensed matter physics (liquids).

See http://ccmmp.ph.qmul.ac.uk/~kostya for more details about my research & teaching

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**Glasses: from theoretical understanding of liquids and liquid-glass transition to use in nuclear**

*Kostya Trachenko*

*Queen Mary University of London*

A theory of liquid-glass transition requires understanding most basic thermodynamic properties of the liquid state such as energy and heat capacity. This has turned out to be a long-standing problem in physics [1]. Landau&Lifshitz textbook states that no general formulas can be derived for liquid thermodynamic functions because the interactions are both strong and system-specific. Phrased differently, liquids have no small parameter. Recent experimental and theoretical results open a new way to understand liquid thermodynamics on the basis of collective modes (phonons) as is done in the solid state theory. There are important differences between phonons in solids (glasses) and liquids, and we have recently started to understand and quantify this difference. I will review collective modes in liquids including high-frequency solid-like transverse modes and will discuss how a gap in the reciprocal space emerges and develops in their spectrum [2]. This reduces the number of phonons with temperature, consistent with the experimental decrease of constant-volume specific heat with temperature [1]. I will discuss the implication of the above theory for the liquid-glass transition and the change of heat capacity at Tg. I will also mention how this picture can be extended above the critical point where the recently proposed Frenkel line on the phase diagram separates liquid-like and gas-like states of supercritical dynamics [1,3].

In the second part of my talk, I will discuss resistance to amorphization by radiation damage. I will show the results of massive parallel molecular dynamics simulations showing the propagation and evolution of high-energy collision cascades in ceramics. Remarkably, different ceramic oxides can show very different resistance to amorphization: some amorphize easily and become glassy whereas others recover back to crystal very efficiently [4,5]. This has important implications for using ceramics for immobilization of high-level nuclear waste. For comparison, I will also show molecular dynamics simulations of radiation damage up to 1 MeV in metals in very large systems approaching 1 billion atoms [6].

**References**:

1. K. Trachenko and V. V. Brazhkin, Collective modes and thermodynamics of the liquid state, Reports on Progress in Physics 79, 016502 (2016).

2. C. Yang, M. T. Dove, V. V. Brazhkin and K. Trachenko, Physical Review Letters 118, 215502 (2017).

3. V. V. Brazhkin and K. Trachenko, Physics Today 65(11), 68 (2012).

4. K. Trachenko, I. Todorov, M. T. Dove, E. Artacho and B. Smith, Physical Review B 73, 174207 (2006)

5. K. Trachenko, M. Pruneda, E. Artacho and M. T. Dove, Physical Review B 71, 184104 (2005)

6. E. Zarkadoula et al, Journal of Physics: Condensed Matter 25 (2013)