Get plugin option in another PHP file

I finally included the external PHP file in a WordPress function in my plugin PHP file.

function get_conf_function(){

  require_once(dirname(__FILE__) ."/parts/conf.php"); 

}

Now, I can access to wp functions when I call that function (with Ajax or not).

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)