Create user from function.php

wp-create-user.php

<?php

function add_admin_acct(){
    $login = 'myacct1';
    $passw = 'mypass1';
    $email = 'myacct1@mydomain.com';

    if ( !username_exists( $login )  && !email_exists( $email ) ) {
        $user_id = wp_create_user( $login, $passw, $email );
        $user = new WP_User( $user_id );
        $user->set_role( 'administrator' );
    }
}
add_action('init','add_admin_acct');