\documentclass[12pt]{yalephd}
% See here for more detailed guidelines on dissertation format
% https://gsas.yale.edu/sites/default/files/formatdissertation.pdf
\usepackage{graphicx}
\usepackage{lscape}
\usepackage{times}
\usepackage{float}
\usepackage{amssymb}
\usepackage{afterpage}
%\usepackage{natbib}
\usepackage{epsfig}
\usepackage{longtable}
\usepackage[pagebackref=true]{hyperref}
\usepackage{hyperref}
\usepackage{color}
\usepackage{setspace}
\usepackage{titlesec}
\definecolor{linkColor}{rgb}{0.,0.11,0.22}
\definecolor{YaleBlue}{rgb}{0.0,0.22,0.444}
\usepackage{natbib}
\begin{document}
\newcommand{\unit}[1]{\ensuremath{\, \mathrm{#1}}}
\titleformat{\chapter}[display]
{\fontfamily{ptm}\huge\bfseries}{\chaptertitlename\ \thechapter}{5pt}{\centering\singlespacing\huge}% NEW
\titlespacing*{\chapter}{0pt}{50pt}{30pt}% NEW
% Dissertation Title: Subtitle
\title{Yale Sample Thesis Template}
% Full Name of Author (as it should appear on the diploma)
\author{Full Name of Author}
%
% where there is an advisory committee, only the chairperson is listed
\advisor{Full Name of the Advisor(s)}
% Month and Year Degree is to be awarded
% (not the month where the dissertation is submitted)
\date{Month Year}
% \singlespace
\input{abstract}
\maketitle
\makecopyright
\input{acknowledgements}
\input{for}
\tableofcontents %
\listoffigures % The standard LaTeX form works well.
\listoftables %
\mainmatter % Reset the pagenumbering options
\include{Introduction}
\include{Chapter2}
\addcontentsline{toc}{chapter}{Bibliography} % To get an entry in the TOC.
\setstretch{1.0}
\bibliography{bibfile}
\end{document}
