List of POTCAR symbols.

def potcar_symbols(self):
        """
        List of POTCAR symbols.
        """
        elements = self.poscar.site_symbols
        potcar_symbols = []
        settings = self._config_dict["POTCAR"]

        if isinstance(settings[elements[-1]], dict):
            for el in elements:
                potcar_symbols.append(settings[el]['symbol']
                                      if el in settings else el)
        else:
            for el in elements:
                potcar_symbols.append(settings.get(el, el))

        return potcar_symbols