Crystal structure evolution and superconductivity of the ternary hydride <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CSH</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> under pressure

Under high-pressure conditions, the changes of atomic arrangement and stacking of the lattice structures lead to enhanced electronic correlation effect and even superconductivity. Motivated by a recent experimental demonstration of pressure-induced superconductivity in a C-S-H system, in this work, we construct a ${\mathrm{CSH}}_{3}$ system via simple combining of ${\mathrm{H}}_{3}\mathrm{S}$ and C to study the crystal structural evolution and possible superconductivity at high pressure using first-principles calculations. We predicted the trigonal and orthorhombic crystal structures of ${\mathrm{CSH}}_{3}$ under pressure, with the space groups $R\text{\ensuremath{-}}3m, Pbcm$, and $Pmmn$, respectively. We find that the trigonal $R\text{\ensuremath{-}}3m$ phase transform to the orthorhombic $Pbcm$ phase at 210 GPa, at which the volume of ${\mathrm{CSH}}_{3}$ phases drops by $\ensuremath{\sim}7%$. Due to large the electronic density of states of the H component near the Fermi level, the ${T}_{c}$ is higher in the $Pbcm$ and the $Pmmn$ phases than in the $R\text{\ensuremath{-}}3m$ phase. A ${T}_{c}$ as high as 98 K is found for the $Pbcm$ phase at 250 GPa.