First-Principle Studies of the Vibrational Properties of Carbonates under Pressure

Abstract

Using the density functional theory with the hybrid functional B3LYP and the basis of localized orbitals of the CRYSTAL17 program code, the dependences of the wavenumbers of normal long-wave ν vibrations on the P(GPa) pressure ν(cm−1) = ν0 + (dv/dP)·P + (d2v/dP2)·P and structural parameters R(Å) (R: a, b, c, RM-O, RC-O): ν(cm−1) = ν0 + (dv/dR) − (R − R0) were calculated. Calculations were made for crystals with the structure of calcite (MgCO3, ZnCO3, CdCO3), dolomite (CaMg(CO3)2, CdMg(CO3)2, CaZn(CO3)2) and aragonite (SrCO3, BaCO3, PbCO3). A comparison with the experimental data showed that the derivatives can be used to determine the P pressures, a, b, c lattice constants and the RM-O metal-oxygen, and the RC-O carbon-oxygen interatomic distances from the known Δν shifts. It was found that, with the increasing pressure, the lattice constants and distances R decrease, and the wavenumbers increase with velocities the more, the higher the ν0 is. The exceptions were individual low-frequency lattice modes and out-of-plane vibrations of the v2-type carbonate ion, for which the dependences are either nonlinear or have negative dv/dP (positive dv/dR) derivatives. The reason for this lies in the properties of chemical bonding and the nature of atomic displacements during these vibrations, which cause a decrease in RM-O and an increase in RC-O.

Chemical Bonding Effects and Physical Properties of Noncentrosymmetric Hexagonal Fluorocarbonates ABCO3F (A: K, Rb, Cs; B: Mg, Ca, Sr, Zn, Cd)

“…However, B3LYP still remains the best compromise between a small number of empirical adjustable parameters (three) and a wide range of highly-accurate properties. In [ 26 , 27 ], the authors were able to calculate the vibrational properties of alkaline-earth metal carbonates.…”

Ab initio исследования влияния давления на структуру, электронные и упругие свойства карбонатов щелочных--щелочно-земельных металлов

“…Расчеты проводились в обобщенно-градиентном приближении с РВЕ функционалом [21]. Использовались также градиентный функционал PBESOL [22], гибридный PBESOL0, с обменно-корреляционным функционалом [22] и 25% обменом по Хартри-Фоку, а также гибридный функционал B3LYP, который сочетает в себе 20% обмен по Хартри-Фоку с обменным функционалом BECKE [23] и корреляционным функционалом LYP [24], который ранее [25,26] хорошо зарекомендовал себя в расчетах колебательных свойств карбонатов щелочноземельных металлов. Обратное пространство дискретизируется с использованием сетки Монкхорста-Пака [27] с 216 независимыми k-точками в неприводимой части зоны Бриллюэна.…”

Pressure-Driven Abnormal Emission Blue-Shift of Lead-Free Halide Double Perovskite Cs2AgInCl6 Nanocrystals

“…To overcome these challenges, much effort has been spent to find environmentally friendly and stable halide perovskites. − For the substitution of Pb, several Pb-free perovskites have been discovered in the past few years. , Among these compounds, Bi- and Ag-based halide double perovskites (DPs) without Pb have been proposed and synthesized in recent years as stable and environmentally friendly alternatives. , However, these Bi- and Ag-based DPs show indirect band gaps. Indirect band gap materials are not suitable for thin-film photovoltaic applications, because an indirect band gap implies weak oscillations that cause optical absorption and radiative recombination .…”

“…As reported, high-pressure technology can be a clean tool for adjusting the lattice parameters and electronic configuration of materials and was used to change the various physical and chemical properties of materials without introducing impurities. , In recent years, conventional halide perovskites under compression have been widely studied, and various new phenomena have been reported, such as pressure-induced amorphization, metallization, band gap modulation, , and emission enhancement . However, only a few studies of halide DPs under high pressure have been reported thus far. , Using high-pressure methods to explore the structure and properties of Cs 2 AgInCl 6 DP nanocrystals can aid in gaining an atom-level understanding for a fundamental study of such materials.…”