params[nparams].powerp = atof(words[11]);

    params[nparams].powerq = atof(words[12]);

    if (params[nparams].epsilon < 0.0 || params[nparams].sigma <= 0.0 || 

	params[nparams].littlea <= 0.0 || params[nparams].lambda < 0.0 ||

	params[nparams].gamma < 0.0 || params[nparams].costheta > 1.0 || 

	params[nparams].costheta < -1.0 || params[nparams].biga < 0.0 || 

    if (params[nparams].epsilon < 0.0 || params[nparams].sigma < 0.0 || 

	params[nparams].littlea < 0.0 || params[nparams].lambda < 0.0 ||

	params[nparams].gamma < 0.0 || params[nparams].biga < 0.0 || 

	params[nparams].bigb < 0.0 || params[nparams].powerp < 0.0 ||

	params[nparams].powerq < 0.0)

      error->all("Illegal Stillinger-Weber parameter");