[Tex/LaTex] description begins on a new line without indent

beamerdescriptionhorizontal alignmentindentationlists

I am using this method to write description in a new line in beamer,

enter image description here

But how can I remove the indent at the new line so it aligns with the \item[]?

This is what I have right now.

\pdfminorversion=4
\documentclass{beamer}
\usetheme{Madrid}
\usepackage{appendixnumberbeamer}
\usepackage{textpos}
\usepackage{animate}
\usepackage{siunitx}
\usepackage{caption}
\usepackage{subcaption}

\begin{document}

\begin{frame}{title}
  \fontsize{8pt}{9}\selectfont
  \begin{columns}
    \centering
    \column{.7\textwidth}
    \vbox to .8\textheight{%
    \begin{figure}
      \centering
      \begin{subfigure}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{../Fig1}
      \end{subfigure}%\hfill
      \begin{subfigure}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{../Fig2}
      \end{subfigure}\\\vfill
      \begin{subfigure}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{../Fig3}
      \end{subfigure}%\hfill
      \begin{subfigure}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{../Fig4}
      \end{subfigure}%
    \end{figure}
    }%

    \column{.3\textwidth}
    Imperfection in Tx and Rx may cause IQ imbalance and other system error.\\
    \begin{description}[leftmargin=0pt]
    \item[Gain Imbalance] \hfill \\Amplitude is different for I and Q.
    \item[Quadrature Error] \hfill \\Phase between I and Q is not \ang{90}.
    \item[IQ Offset] \hfill \\I and Q are not centered at zero.
    \item[Gain Compression] \hfill \\Distance $d$ between constellation points is power dependent.
    \end{description}

  \end{columns}
\end{frame}

\end{document}

Best Answer

One easy way is to set description width to be equal to -\labelsep; in the following example I made the change local to a frame, but if you move the line

\setbeamersize{description width=-\labelsep}

the change will be global:

\documentclass{beamer}

\begin{document}

{
\setbeamersize{description width=-\labelsep}
\begin{frame}
\begin{description}
\item[First]\mbox{}\\ The first item.
\item[Second]\mbox{}\\ The second item.
\item[Third]\mbox{}\\ The third item.
\end{description}
\end{frame}
}

\end{document}

enter image description here

An with the updated code in the question, there's \begin{description}[leftmargin=0pt], so the string "leftmargin=0pt" is taken as the widest label, overriding the previously defined description width; all that needs to be done is to delete [leftmargin=0pt]. Notice also that I replaced figure with center and subfigure with minipage (there's really no need for neither the figure nor for the subfigure environments in beamer):

\documentclass{beamer}
\usepackage{siunitx}

\begin{document}

{
\setbeamersize{description width=-\labelsep}
\begin{frame}{title}
  \fontsize{8pt}{9}\selectfont
  \begin{columns}
    \column{.7\textwidth}
    \vbox to .8\textheight{%
    \begin{center}
      \begin{minipage}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{example-image-a}
      \end{minipage}%\hfill
      \begin{minipage}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{example-image-b}
      \end{minipage}\\\vfill
      \begin{minipage}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{example-image-c}
      \end{minipage}%\hfill
      \begin{minipage}[b]{.5\textwidth}
        \centering
        \includegraphics[width=\textwidth]{example-image-a}
      \end{minipage}%
      \end{center}
    }%

    \column{.3\textwidth}

    Imperfection in Tx and Rx may cause IQ imbalance and other system error.\\
    \begin{description}
    \item[Gain Imbalance] \hfill \\Amplitude is different for I and Q.
    \item[Quadrature Error] \hfill \\Phase between I and Q is not \ang{90}.
    \item[IQ Offset] \hfill \\I and Q are not centered at zero.
    \item[Gain Compression] \hfill \\Distance $d$ between constellation points is power dependent.
    \end{description}

  \end{columns}
\end{frame}
}

\end{document}

enter image description here

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