Fit model: Two-Youkawa potential

Parameters:

parameter |
description |

F_rad |
radius (2*F_rad is the effective diameter) |

S_phi |
volume fraction |

S_Z1 |
potential 1 |

S_K1 |
positive for attraction, negative for repulsion |

S_Z2 |
potential 2 |

S_K2 |
positive for attraction, negative for repulsion |

Remarks:

Potential From: V(r)/(kB*T)=-K1*exp(-Z1*(r-1))/r - K2*exp(-Z2*(r-1))/r

Package taken from: www.che.udel.edu/cns/pdf/TYSQ21.zip

Please cite the paper, Yun Liu, Wei-Ren Chen, Sow-Hsin Chen, "Cluster Formation in Two Yukawa Fluids", Journal of Chemical Physics 122, 044507 (2005), if you use the results produced by this code.

Remarks by the author:

1. Can K1 and K2 be zero?

No. The codes assume that there must be two Yukawa terms. Therefore, if you want to make one or both of them zero, you can only do it by making them very small values.

2. Can I make Z1 and Z2 very large number?

In principle, the answer is Yes. However, this is very subtle. In general, always try to make Z1 > Z2, when you want to try a very large number, such as Z > 20. This is because that Z1 and Z2 are treated in an asymmetric way in the computer codes. In order to make the calculation more accurate, Z1 > Z2 will be a nice trick. In general, when Z < 20, it dose not matter. When Z > 25, sometimes the intermediate results of this codes may run into the limit of the largest number that a computer can handle. Therefore, results may potentially become less reliable. Hence, the check of g(r) becomes very important in those situations. So far, I did not find out any limitation of the value of K except that they can not be zero.

3. Can Z1 and Z2 be equal?

Z1 and Z2 should not be equal. If they are equal, there is essentially only one Yukawa term. Therefore, the algorithm designed for two term Yukawa potential will fail. However, the codes can handle cases that Z1 and Z2 have only very small differences.

References:

Yun Liu, Wei-Ren Chen, Sow-Hsin Chen, J. Chem. Phys. 122, 044507 (2005)