Phonon Life-times from first principles self consistent lattice dynamics

Phonon lifetime calculations from first principles usually rely on time consuming molecular dynamics calculations, or density functional perturbation theory (DFPT) where the zero temperature crystal structure is assumed to be dynamically stable. Here a new and effective method for calculating phonon lifetimes from first principles is presented, not limited to crystal structures stable at 0 K, and potentially much more effective than most corresponding molecular dynamics calculations. The method is based on the recently developed self consistent lattice dynamical method and is here tested by calculating the bcc phase phonon lifetimes of Li, Na, Ti and Zr, as representative examples.Comment: 4 pages, 4 figur

Electronic Structure and Lattice Dynamics of Elements and Compounds

The elastic constants of Mg(1-x)AlxB2 have been calculated in the regime 0<x<0.25. The calculations show that the ratio, B/G, between the bulk- and the shear-modulus stays well below the empirical ductility limit, 1.75, for all concentrations, indicating that the introduction of Al will not change the brittle behaviour of the material considerably. Furthermore, the tetragonal elastic constant C’ has been calculated for the transition metal alloys Fe-Co, Mo-Tc and W-Re, showing that if a suitable tuning of the alloying is made, these materials have a vanishingly low C'. Thermal expansion calculations of the 4d transition metals have also been performed, showing good agreement with experiment with the exception of Nb and Mo. The calculated phonon dispersions of the 4d metals all give reasonable agreement with experiment. First principles calculations of the thermal expansion of hcp Ti have been performed, showing that this element has a negative thermal expansion along the c-axis which is linked to the closeness of the Fermi level to an electronic topological transition. Calculations of the EOS of fcc Au give support to the suggestion that the ruby pressure scale might underestimate pressures with ~10 GPa at pressures ~150 GPa. The high temperature bcc phase of the group IV metals has been calculated with the novel self-consistent ab-initio dynamical (SCAILD) method. The results show good agreement with experiment, and the free energy resolution of < 1 meV suggests that this method might be suitable for calculating free energy differences between different crystallographic phases as a function of temperature

Interplay between effect of Mo and chemical disorder on the stability of beta/beta(o)-TiAl phase

The effect of Mo and chemical disorder on chemical, mechanical and dynamical phase stability of β(bcc)/βo (B2)-TiAl is studied using Density Functional Theory. The ordered βo structure has more negative energy of formation, hence it is chemically more stable than the disordered β structure. Our calculations further suggest that the ordered structure is mechanically unstable for Mo concentrations View the MathML source<≈4at.%. Surprisingly, the disordered β phase is found to be mechanically stable regardless the Mo content. It is therefore concluded that the chemical disorder and the Mo alloying play a similar role in the stabilisation of β/βo-TiAl. This trend is further confirmed by studying phonon and electronic density of states. Finally, the ordered βo structure is shown to sit in a saddle point of a potential energy surface. A barrier-less transformation path βo→γ exists, allowing for a spontaneous transformation from the symmetry stabilised βo to the ground state γ-phase.Web of Science61908

Uppsala Master Theses in Computing Science 252 Examensarbete DV3 2004-01-25 ISSN 1100-1836 Development of User Interface for Simulation Program of Material Calculations

Mjukvara for forsta princip-berakningar av materialegenskaper har utvecklats och anvands dagligen av forskare vid fysiska institutuionen, Uppsala Universitet, och vid flera forskningslaboratorier och universitet runt om i varlden. Denna mjukvara bestar av 4 olika program som alla kraver indata i textformat, dock pa ett mycket strikt satt. Framstallandet av indata gors i nulaget for hand, och tar ansenlig tid. Nagon riktig anvandarhandledning till detta program finns inte och syftet med detta arbete har varit att forenkla anvandandet av programmet genom att utveckla ett separat program som producerar indatafiler. Supervisor: Petros Souvatzis Examinator: Olle Eriksson Passed: Pretext This project was done as a Master&apos;s Thesis in Computing Science by Angela Sjoholm, student at Uppsala University. The project was carried out at Institute of Physics, Angstrom Laboratories, Uppsala University and the Department of Physics and Measurement Technology, Linkoping University. I want to thank everyone at the department of Condensed Matter Theory for their help and support. Special thanks to Petros Souvatzis for guiding me through the jungle of physics. Thanks to Jan Gulliksen for advising me regarding hci. Summary Software performing first principle calculations for material properties has been developed and is used daily by scientists at the Institution of Physics, Uppsala University, and at several other laboratories and universities around the world. This software consists of 4 di#erent programs that all demand input on a text format, though in a very strict way. Producing the input, currently done manually, takes considerable time. There exists no real user manual to this program and the aim of this project has been to improve the usability of the program by developing a sep..

Femtosecond bond breaking and charge dynamics in ultracharged amino acids

Historically, structure determination of nanocrystals, proteins, and macromolecules required the growth of high-quality crystals sufficiently large to diffract X-rays efficiently while withstanding radiation damage. The development of the X-ray free-electron laser has opened the path toward high resolution single particle imaging, and the extreme intensity of the X-rays ensures that enough diffraction statistics are collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. In this study, we use first-principles based methods to study the impact of radiation induced ionization of six amino acids on the reconstruction process. In particular, we study the fragmentation and charge rearrangement to elucidate the time scales involved and the characteristic fragments occurring