SMTP Error: Could not authenticate. Message could not be sent.

global $error;
$mail = new PHPMailer();
$mail->IsSMTP();
$mail->SMTPDebug = 0;
$mail->SMTPAuth = true;
$mail->SMTPSecure = 'ssl';
$mail->Host = 'smtp.gmail.com';
$mail->Port = 465;
$mail->Username = "@gmail.com";
$mail->Password = "";
$mail->SetFrom("", "");