The computation of free energy of TIP4P water using expanded ensemble method
利用扩展系综法计算水的自由能

The free energy of the TIP4P water is computed by expanded ensemble method,which allows us to calculate absolute free energies with a high precision for arbitrary systems using a relative simple computational scheme.The free energy of NVT ensemble of TIP4P water is -21.485±0.035kJ/mol,which is in accordance with the r esults obtained by using other method.A method for choosing crucial parameters ( balance factors)is proposed.