Absolute NMR shielding scales in methyl halides obtained from experimental and calculated nuclear spin-rotation constants

The nonrelativistic ``Ramsey-Flygare relationship'' is the most used procedure to obtain semiexperimental nuclear magnetic resonance (NMR) absolute shieldings by a correspondence between NMR ($\mathbit{\ensuremath{\sigma}}$) and spin-rotation constants ($\mathbit{M}$). One of its generalizations relativistic framework known as M-V model, which was proposed few year ago some authors present work right now only applied linear molecules. This model includes terms that do not have counterparts also include paramagnetic contribution shielding nuclei in free atoms. All this ensures results fit quite well with those four-component (4c) calculations. first application nonlinear molecules, like methyl halides or ${\mathrm{CH}}_{3}X$ molecules ($X=\mathrm{F}$, Cl, Br, I), given here. analysis each electronic mechanism $\mathbit{\ensuremath{\sigma}}$ shows their electron correlation effects are strongly related same $\mathbit{M}$. By including experimental data $M$ accurately taken into account for values $\mathbit{\ensuremath{\sigma}}$. Calculations ${\mathbit{M}}_{Y}$ ${\mathbit{\ensuremath{\sigma}}}_{Y}$ ($Y=\mathrm{H}$, C, $X$) were carried out within response formalism at random-phase level approach density functional theory both 4c frameworks. best fits calculations $\mathbit{M}$ obtained from 4c-PBE0 all cases, but ${M}_{\ensuremath{\parallel},\mathrm{Cl}}$, suggests revision available may be necessary. There an additional advantage using model: one can indirectly calculate open-shell atoms, cannot moment applying methods.