I am a vimwiki user, but now I want to use the vim-pandoc tools to create PDF from markdown files of the wiki. The problem is that the function of omnicomplete, for bib cites, of vim-pandoc does not work when I have installed vimwiki.

solution: add init function to onenter command

OR, if using deoplete to complete:

call deoplete#custom#var('omni', 'input_patterns', {
  \'pandoc': '@\w*',
  \})
call deoplete#custom#var('omni', 'functions', {
  \'pandoc': 'pandoc#completion#Complete',
  \})

To enable omnifunc completion for pandoc, invoked on @someletters. If your bib-file is large, it will take a second.

(you can also get the completions from multiple functions, using a dict in the functions: pandoc definition, e.g. ['pandoc#completion#Complete', 'wiki#links#aggregate'] )