To resolve this problem, it is recommened to do the following operations.
Find the location: $HOME/texmf/tex/latex/
Place document class files (extension .cls), packages and any other custom style files for use by LaTeX (extensions .sty or .tex) into this directory. If custom bibtex style files (extension .bst) have been provided, place these into a similar tree of the form $HOME/texmf/bibtex/bst/
An extra and important step: whenever we add new files to the texmf tree, be sure to run texhash. For efficiency reasons, TeX does not search for files, but only consults the ls-R database; if a (non-standard) file is not listed in this database, TeX will not find it.