Execute jQuery function from javascript

Execute jQuery function from javascript

Please excuse my English and my ignorance in jquery

I have a function javascript which validate information.
function validateLogin() {
   if ( document.getElementById("login").value == "fail" )
      .... i need show  a modal window to login ....
  }
}

I trying use jQuery, but.... i don't know how call the jQuery function....for example....

$(document).ready(function() {  
        $('#div_login').click(function(e) {
            alert("HELLO, Log in please!!!!");
        });
});

How i can call the event click of #div_login????