vertical alignment in texstudio - latex

Question

I am making a table with texstudio, and I have trouble with vertical alignment of the texts. When I have \hline, the text crosses the line.
Here is the code:
\documentclass{article}
\usepackage{siunitx}
\begin{document}
\begin{tabular}{lcccc}
\hline\hline
& \textbf{$d_{(O_{1}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{2}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{3}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{\bot}-Zn/Mg)}(\SI{}{\angstrom})$} \\[1mm]
\hline
\textbf{Pure HB-NWs} & & & & \\
\hline\hline
\end{tabular}
\end{document}
And I have also enclosed the undesired result to make my point clear.

Answer 1

I would suggest using the booktabs package which addresses rules and lines in tables quite well. See its documentation for some notes on table formatting and how to used it. In short, adding
\usepackage{booktabs}
to your preamble will let you use a number of new commands for rules in tables:
\toprule
\midrule
\bottomrule
combining these with your example gives a table looking as follows:
or, if you insist on using double rules at top and bottom:
In both cases I don't see the need for your additional '[1em]' space below the top line - without it things would look like this:
,
This will generate a pdf with all three examples to allow easy comparison:
\documentclass{article}
\usepackage{siunitx}
\usepackage{booktabs}
\begin{document}
Using \emph{booktabs} style rules:\\\vskip\baselineskip
\begin{tabular}{lcccc}
\toprule
& \textbf{$d_{(O_{1}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{2}-Zn/Mg)}(\SI{}{\angstrom})$} \\[1mm]
\midrule
\textbf{Pure HB-NWs} & & & & \\
\bottomrule
\end{tabular}
\vskip\baselineskip
also works without the additional `[1mm]' spacing at the bottom of the line:
\vskip\baselineskip
\begin{tabular}{lcccc}
\toprule
& \textbf{$d_{(O_{1}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{2}-Zn/Mg)}(\SI{}{\angstrom})$} \\
\midrule
\textbf{Pure HB-NWs} & & & & \\
\bottomrule
\end{tabular}
\vskip\baselineskip
\vskip\baselineskip
Using \emph{double rules}:
\vskip\baselineskip
\begin{tabular}{lcccc}
\midrule\midrule
& \textbf{$d_{(O_{1}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{2}-Zn/Mg)}(\SI{}{\angstrom})$} \\[1mm]
\midrule
\textbf{Pure HB-NWs} & & & & \\
\midrule\midrule
\end{tabular}
\vskip\baselineskip
and again without the additional `[1mm]' spacing at the bottom of the line:
\vskip\baselineskip
\begin{tabular}{lcccc}
\midrule\midrule
& \textbf{$d_{(O_{1}-Zn/Mg)}(\SI{}{\angstrom})$}
& \textbf{$d_{(O_{2}-Zn/Mg)}(\SI{}{\angstrom})$} \\
\midrule
\textbf{Pure HB-NWs} & & & & \\
\midrule\midrule
\end{tabular}
\end{document}
On a side note: the 'siunitx' package you're using provides a '\si' command specifically for printing only units, rather than using the '\SI' command with an empty argument; i.e. you might want to use the following:
\si{\angstrom}
rather than:
\SI{}{\angstrom}