Can the liquid system relax faster than its individual molecules?—Negative dipole correlations revealed by molecular dynamics simulations

Abstract Dielectric studies of many liquids have revealed their ability to develop subtle structural order, reflected in a Kirkwood correlation factor, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>g</mml:mi> <mml:mrow> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> , dropping below unity. In this letter, we perform molecular dynamics simulations and, for the first time, examine the reorientational dynamics of a system characterized by a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>g</mml:mi> <mml:mrow> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> value significantly lower than one. To this end, we introduce a novel and breakthrough model of a polar quasi-real molecule, the 2RMSG, that is constructed by merging polar rhombus-like molecule (Koperwa et al 2020 Sci. Rep. 10 283 and Koperwas et al 2020 Phys. Rev. Lett. 129 025501), with a non-polar one that is complemented with a side group. Our investigations reveal that systems with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>g</mml:mi> <mml:mrow> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>&lt;</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:math> exhibit dipole–dipole cross-correlations that remain negative throughout the entire time until their decay. By extracting these cross-correlations from the macroscopic correlation functions typically observed in standard experiments, we demonstrate that the overall relaxation of the system proceeds faster than the relaxation of its microscopic self- and cross-components.