How to use \textsc{} in Section or Subsection?

Question

I am trying to add \textsc{text} in my subsection title

i tried \subsection{\textsc{Born-Oppenheimer} approximation}

but no changement appeared, the text Born-Oppenheimer is not affected by the command \textsc{}. It is still in normal case.

note: i am using the book class: \documentclass[11pt,a4paper]{book}

Do you know how i can fix this problem?

the document setup:

\documentclass[11pt,a4paper]{book}
\usepackage[utf8]{inputenc}
\usepackage{babel}[english]
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{lscape}
\usepackage{rotating}
\usepackage{multirow}
\usepackage{array}
\usepackage{arydshln}
\usepackage{appendix}
\usepackage{floatrow}

\usepackage{mathtools}
\usepackage{ mathrsfs }
\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary{arrows}
\usepackage{pgfplots}
\usepackage{bigdelim}
\usepackage{cite}
\usepackage{microtype}
\usepackage{hhline}
\pgfplotsset{compat=1.3} 
\usepackage[left=3.50cm, right=2.50cm, top=4.00cm]{geometry}
\raggedbottom
\usepackage{hyperref}
\usepackage{wrapfig}
\hypersetup{colorlinks,%
    citecolor=black,%
    filecolor=black,%
    linkcolor=black,%
    urlcolor=black
}
\usepackage{subcaption}
\usepackage{csquotes}
\usepackage{minitoc}
\usepackage{xcolor}
\usepackage{hyperref}
\hypersetup{colorlinks=true, linkbordercolor=red,linkcolor=red}
\usepackage{enumitem}
\usepackage{pifont}
\usepackage{soulutf8}
\usepackage{xspace}
\usepackage[Lenny]{fncychap}
\begin{document}
\stepcounter{chapter}
\stepcounter{section}
\subsection{\textsc{Born-Oppenheimer} approximation}
\end{document}

Answer 1

I'm guessing you're using a font -- possibly Computer Modern -- that doesn't provide a bold-smallcaps weight-shape glyph combination. If that's the case, you need to input

\subsection{\textsc{\textmd{Born-Oppenheimer}} approximation}

to get non-bold (aka "medium weight") smallcap letters for "Born-Oppenheimer".

To employ bold-smallcaps, you need to employ a font family that provides this particular combination. One such font family is Times (New) Roman.

\documentclass[11pt,a4paper]{book}
\usepackage{newtxtext,newtxmath} % Times Roman clone
\begin{document}
\stepcounter{chapter} % just for this example
\stepcounter{section}
\subsection{\textsc{\textmd{Born-Oppenheimer}} approximation}
\subsection{\textsc{Born-Oppenheimer} approximation}
\end{document}