Use get_the_post_thumbnail
with a new WP_Query.
<?php
if ( has_post_thumbnail()) {
$large_image_url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'large');
echo '<a href="' . $large_image_url[0] . '" title="' . the_title_attribute('echo=0') . '" >';
echo get_the_post_thumbnail($post->ID, 'thumbnail', array('class' => 'aligncentre'));
echo '</a>';
}
?>