scholarly journals Polymorph exploration of bismuth stannate using first-principles phonon mode mapping

2020 ◽  
Vol 11 (30) ◽  
pp. 7904-7909
Author(s):  
Warda Rahim ◽  
Jonathan M. Skelton ◽  
Christopher N. Savory ◽  
Ivana R. Evans ◽  
John S. O. Evans ◽  
...  
Keyword(s):  
First Principles ◽  
Phonon Mode ◽  
Metastable Phases ◽  
Ternary Oxide ◽  
Complex Materials ◽  
Mapping Approach ◽  
Mode Mapping

Using a phonon mode-mapping approach, we recover the known experimental phases of the ternary oxide Bi2Sn2O7 and identify three new metastable phases, highlighting the utility of the method for polymorph prediction on many other complex materials.

scholarly journals Polymorph Exploration of Bismuth Stannate Using First-principles Phonon Mode Mapping

2020 ◽  
Author(s):  
Warda Rahim ◽  
Jonathan Skelton ◽  
Christopher Savory ◽  
Ivana Radosavljevic Evans ◽  
John S. O. Evans ◽  
...  
Keyword(s):  
First Principles ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Phonon Mode ◽  
Energy Surface ◽  
Global Minima ◽  
Transition Pathways ◽  
Complex Crystal ◽  
Mode Mapping ◽  
Difficult Cases

In this work, we present a new unbiased and efficient quantum chemical method for exploring the potential energy surface of complex crystal structures using theoretically rigorous phonon mode-mapping approach. The method successfully recovers the known experimental phases of the pyrochlore-based Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub>, one of the most difficult cases in structural chemistry, which highlights its utility for searching possible transition pathways and identifying global minima for many other challenging systems.<p></p>

scholarly journals Polymorph Exploration of Bismuth Stannate Using First-principles Phonon Mode Mapping

2020 ◽  
Author(s):  
Warda Rahim ◽  
Jonathan Skelton ◽  
Christopher Savory ◽  
Ivana Radosavljevic Evans ◽  
John S. O. Evans ◽  
...  
Keyword(s):  
First Principles ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Phonon Mode ◽  
Energy Surface ◽  
Global Minima ◽  
Transition Pathways ◽  
Complex Crystal ◽  
Mode Mapping ◽  
Difficult Cases

In this work, we present a new unbiased and efficient quantum chemical method for exploring the potential energy surface of complex crystal structures using theoretically rigorous phonon mode-mapping approach. The method successfully recovers the known experimental phases of the pyrochlore-based Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub>, one of the most difficult cases in structural chemistry, which highlights its utility for searching possible transition pathways and identifying global minima for many other challenging systems.<p></p>

scholarly journals Free Energy of Metals from Quasi-Harmonic Models of Thermal Disorder

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 195
Author(s):  
Pavel A. Korzhavyi ◽  
Jing Zhang
Keyword(s):  
Free Energy ◽  
First Principles ◽  
Density Functional ◽  
Helmholtz Free Energy ◽  
Complex Materials ◽  
Predictive Capability ◽  
Temperature Dependent ◽  
Disordered Alloys ◽  
Thermal Disorder ◽  
Structure Calculations

A simple modeling method to extend first-principles electronic structure calculations to finite temperatures is presented. The method is applicable to crystalline solids exhibiting complex thermal disorder and employs quasi-harmonic models to represent the vibrational and magnetic free energy contributions. The main outcome is the Helmholtz free energy, calculated as a function of volume and temperature, from which the other related thermophysical properties (such as temperature-dependent lattice and elastic constants) can be derived. Our test calculations for Fe, Ni, Ti, and W metals in the paramagnetic state at temperatures of up to 1600 K show that the predictive capability of the quasi-harmonic modeling approach is mainly limited by the electron density functional approximation used and, in the second place, by the neglect of higher-order anharmonic effects. The developed methodology is equally applicable to disordered alloys and ordered compounds and can therefore be useful in modeling realistically complex materials.

scholarly journals A First-Principles Exploration of NaxSy Binary Phases at 1 atm and Under Pressure

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 441 ◽  
Author(s):  
Nisha Geng ◽  
Tiange Bi ◽  
Niloofar Zarifi ◽  
Yan Yan ◽  
Eva Zurek
Keyword(s):  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Elemental Sulfur ◽  
Density Functional Theory Calculations ◽  
Metastable Phases ◽  
Van Der Waals Interactions ◽  
Two Dimensional ◽  
Functional Theory ◽  
Battery Materials

Interest in Na-S compounds stems from their use in battery materials at 1 atm, as well as the potential for superconductivity under pressure. Evolutionary structure searches coupled with Density Functional Theory calculations were employed to predict stable and low-lying metastable phases of sodium poor and sodium rich sulfides at 1 atm and within 100–200 GPa. At ambient pressures, four new stable or metastable phases with unbranched sulfur motifs were predicted: Na2S3 with C 2 / c and Imm2 symmetry, C 2 -Na2S5 and C 2 -Na2S8. Van der Waals interactions were shown to affect the energy ordering of various polymorphs. At high pressure, several novel phases that contained a wide variety of zero-, one-, and two-dimensional sulfur motifs were predicted, and their electronic structures and bonding were analyzed. At 200 GPa, P 4 / m m m -Na2S8 was predicted to become superconducting below 15.5 K, which is close to results previously obtained for the β -Po phase of elemental sulfur. The structures of the most stable M3S and M4S, M = Na, phases differed from those previously reported for compounds with M = H, Li, K.

scholarly journals First principles-based multiparadigm, multiscale strategy for simulating complex materials processes with applications to amorphous SiC films

2015 ◽  
Vol 142 (17) ◽  
pp. 174703 ◽  
Author(s):  
Saber Naserifar ◽  
William A. Goddard ◽  
Theodore T. Tsotsis ◽  
Muhammad Sahimi
Keyword(s):  
First Principles ◽  
Complex Materials ◽  
Amorphous Sic ◽  
Sic Films

Novel elastic evolution of carbide Mo2Ga2C under pressure: Ab initio theoretical investigation

2019 ◽  
Vol 33 (30) ◽  
pp. 1950358
Author(s):  
Rui Wu ◽  
Hai-Chen Wang ◽  
Yan Yang ◽  
Li Ma ◽  
Shan Jiang ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Elastic Constants ◽  
Pressure Dependence ◽  
First Principles ◽  
Phonon Mode ◽  
First Principles Calculation ◽  
Max Phases ◽  
Transverse Acoustic ◽  
Phonon Structure

The pressure dependence of elastic properties of Mo2Ga2C is studied via first-principles calculation. The present investigation shows that differing from other MAX phases, in Mo2Ga2C the [Formula: see text] is larger than [Formula: see text], because of the strong Ga–Ga interlayer bonds along [Formula: see text]-axis. Moreover, under pressure, the [Formula: see text] increases more rapidly, originating from the faster strengthening of Ga–Ga bonds. Interestingly, elastic constants [Formula: see text] soften under high pressure (more than 20 GPa). Especially, the calculated phonon structure demonstrates that transverse acoustic (TA) phonon mode also softens under pressure, implying possible phase transition. The reduction of [Formula: see text] and softening of phonon mode are attributed to significantly weakened Mo–Mo interaction in contrast to the strengthening of Ga–Ga bonds under high pressure. Our present results further indicate that Mo2Ga2C is more ductile under pressure.

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