English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Density-functional simulations are used to calculate structural propertiesand high-symmetry phonons of the hypothetical cubic phase, the stableorthorhombic phase and an intermediate tetragonal phase of magnesium silicateperovskite. We show that the structure of the stable phase is well described byfreezing in a small number of unstable phonons into the cubic phase. We use thefrequencies of these unstable modes to estimate transition temperatures forcubic--tetragonal and tetragonal--orthorhombic phase transitions. These areinvestigated further to find that the coupling with the strain suggests thatphonons give a better representation than rigid unit modes. The phonons of anintermediate tetragonal phase were found to be stable except for two rotationalmodes. The eigenvectors of the most unstable mode of each of the cubic andtetragonal phases account for all the positional parameters of the orthorhombicphase. The phase boundary for the orthorhombic--tetragonal transitionintersects possible mantle geotherms, suggesting that the tetragonal phase maybe present in the lower mantle.Comment: 16 pages, REVTEX, 7 postscript figures (Fig 1 very large, contact  Authors if required); submitted to Physics and Chemistry of Mineral

Ab initio studies of structural instabilities in magnesium silicate perovskite