The code at the end gives
As you can see, \widehat and \widetilde give good result, but \overline looks bad on some characters, especially for A, I and J. What commands or workarounds can solve this problem, please.
\documentclass[10pt, a4paper]{article} \begin{document} \noindent $ \overline{A} \ \overline{I} \ \overline{J} $ \\ $ \widetilde{A} \ \widetilde{I} \ \widetilde{J} $ \\ $ \widehat{A} \ \widehat{I} \ \widehat{J} $ \\ \end{document} You can use Henrik Vogt's code in an answer to a similar question:
\documentclass{article} \usepackage[T1]{fontenc} \usepackage{amsmath} \makeatletter \newcommand*\rel@kern[1]{\kern#1\dimexpr\macc@kerna} \newcommand*\widebar[1]{% \begingroup \def\mathaccent##1##2{% \rel@kern{0.8}% \overline{\rel@kern{-0.8}\macc@nucleus\rel@kern{0.2}}% \rel@kern{-0.2}% }% \macc@depth\@ne \let\math@bgroup\@empty \let\math@egroup\macc@set@skewchar \mathsurround\z@ \frozen@everymath{\mathgroup\macc@group\relax}% \macc@set@skewchar\relax \let\mathaccentV\macc@nested@a \macc@nested@a\relax111{#1}% \endgroup } \makeatother \begin{document} \[ \widebar{A}\ \widebar I\ \widebar J\]% \[ \widetilde{A}\ \widetilde I\ \widetilde J\]% \[ \widehat{A}\ \widehat I\ \widehat J\]% \end{document} 
\overlinecommands. It might be helpful.