Set the values of the ABINIT variables in the input file. Return dict with old values.

def set_vars(self, *args, **kwargs):
        """
        Set the values of the ABINIT variables in the input file. Return dict with old values.
        """
        kwargs.update(dict(*args))
        old_values = {vname: self.input.get(vname) for vname in kwargs}
        self.input.set_vars(**kwargs)
        if kwargs or old_values:
            self.history.info("Setting input variables: %s" % str(kwargs))
            self.history.info("Old values: %s" % str(old_values))

        return old_values