natbib: Working Paper and DOI in Bibliography

Question

I am having two problems in Bibliography. First, when I cite some working paper, complete information of working paper is not shown and only following information is displayed.

Schwarcz, S. L. (2008). Systemic Risk.

However, the information about publisher, working paper series and url are available in the bib file. Second, DOI and URL of references are not displayed in the bibliography. A minimal working example is given below:

   \documentclass[12pt,twoside,openany]{book}
   \usepackage{authblk}
   \usepackage{titlesec}
   \usepackage[T1]{fontenc}
   \usepackage{times}
   \usepackage[latin9]{inputenc}
   \usepackage[english]{babel}
   \usepackage[round,nonamebreak]{natbib}

   \begin{document}
    \author{Ahmed Arif}
    \title{A Book}

   \chapter{Introduction}
   This is introduction chapter \citep{Schwarcz2008}. The literature is        cited here \citet{Cebenoyan2004}.

   \bibliographystyle{apa}
   \bibliography{library}
   \end{document}

The entries availabe in the bib file are given below. The bib file is obtained from mendley.

    @article{Cebenoyan2004,
    author = {Cebenoyan, A.Sinan and Strahan, Philip E},
    doi = {10.1016/S0378-4266(02)00391-6},
    file = {:C$\backslash$:/Users/Ahmed Arif/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Cebenoyan, Strahan - 2004 - Risk management, capital structure and lending at banks.pdf:pdf},
    issn = {03784266},
    journal = {Journal of Banking {\&} Finance},
    keywords = {7 december 2001,at the x international,bank risk management,banking and finance held,in rome on 5,loan sales,this paper was presented,tor vergata conference on},
    month = {jan},
    number = {1},
    pages = {19--43},
    title = {{Risk management, capital structure and lending at banks}},
    url = {http://linkinghub.elsevier.com/retrieve/pii/S0378426602003916},
    volume = {28},
    year = {2004}
    }
    @unpublished{Schwarcz2008,
    address = {Durham},
    author = {Schwarcz, Steven L.},
    file = {:C$\backslash$:/Users/Ahmed Arif/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Schwarcz - 2008 - Systemic Risk.pdf:pdf},
    institution = {Duke Law School},
    pages = {193--249},
    series = {Research Paper Series},
    title = {{Systemic Risk}},
    url = {http://papers.ssrn.com/sol3/papers.cfm?abstract{\_}id=1008326},
    year = {2008}
    }

Answer 1

The apa.bst bibliography style file was last modified in 1992 -- 25 [!] years ago. As such, it's not programmed to do anything at all with fields called url and doi. As it looks like you're interested in formatting the bibliography according to APA guidelines -- the current ones, presumably, not the ones from 1992 -- I suggest you use the apacite bibliography style and load the apacite citation management package. Load the package with the option natbibapa to enable natbib-like citation commands such as \citet and \citep.

You should also load the url package, and you should not, under any circumstance, "escape" underscore characters in URL strings unless you want to make the URLs unusable for your readers. Oh, and don't load the times package -- it's totally deprecated. If you need to typeset your document using Times Roman as the main text font, I suggest you load the packages newtxtext and newtxmath.

One more comment about the bib entries, which -- I take it -- were produced by Mendeley: Do check them for errors. For instance, month = {jan}, is an outright error; it should be month = jan,.

\RequirePackage{filecontents}
\begin{filecontents}{library.bib}
@article{Cebenoyan2004,
    author = {Cebenoyan, A. Sinan and Strahan, Philip E.},
    doi = {10.1016/S0378-4266(02)00391-6},
    file = {:C$\backslash$:/Users/Ahmed Arif/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Cebenoyan, Strahan - 2004 - Risk management, capital structure and lending at banks.pdf:pdf},
    issn = {03784266},
    journal = {Journal of Banking \& Finance},
    keywords = {7 december 2001,at the x international,bank risk management,banking and finance held,in rome on 5,loan sales,this paper was presented,tor vergata conference on},
    month = jan,
    number = {1},
    pages = {19--43},
    title = {Risk management, capital structure and lending at banks},
    url = {http://linkinghub.elsevier.com/retrieve/pii/S0378426602003916},
    volume = {28},
    year = {2004}
    }
@unpublished{Schwarcz2008,
    address = {Durham},
    author = {Schwarcz, Steven L.},
    file = {:C$\backslash$:/Users/Ahmed Arif/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Schwarcz - 2008 - Systemic Risk.pdf:pdf},
    institution = {Duke Law School},
    pages = {193--249},
    series = {Research Paper Series},
    title = {Systemic Risk},
    url = {http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1008326},
    year = {2008}
    }
\end{filecontents}

\documentclass[12pt,twoside,openany]{book}
\usepackage{authblk}
\usepackage{titlesec}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{newtxtext,newtxmath} % 'times' is deprecated
\usepackage[english]{babel}

\usepackage{url}
\usepackage[natbibapa]{apacite}
\bibliographystyle{apacite}

\begin{document}
\dots\ \citep{Schwarcz2008} \dots\ \citet{Cebenoyan2004} \dots
\bibliography{library}
\end{document}