Most atheists are not closed minded. In fact, many atheists were once theists, raised in one religion or another, but managed to escape from those religions. These are people who have changed their minds on some fairly important, basic issues. They're already much more open minded than most theists.

Often, theists have a misunderstanding of what it means to be "closed minded". Being closed minded means that one is not open to having one's mind changed, or open to considering new information - neither of which applies to atheists, most of the time. One is not required to automatically accept whatever another person tells him or her.

If one wants to convince an atheist of something, following the standards of science is the appropriate method.

Trying to convince an atheist that a god exists using a snickers bar, with a smiley face chiseled on it, is not bound be terribly effective. It must be a good argument with good evidence to back it up.