If you are having LinkButton then you might be having any OnClick event so you cannot use return false in JavaScript. But if you are not having any server side event for the linkButton then you can write this way.
JavaScript
<script type="text/javascript">
function FocusDiv() {
window.location.hash = '#div1';
return false;
}
</script>
HTML
<asp:LinkButton Text="Focus" runat="server" OnClientClick="return FocusDiv();" />