- #1
ab_kein
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I've seen a lot of articles, where people calculate free Gibbs energy of system using several methods in some sense indirect methods, but I've never seen it is being calculated using its definition:
$$ \Phi=U+pV-TS $$
Imagine a big MD system at its equilibrium in a box with periodic boundary conditions. Now consider a smaller sub-box with walls transparent for particles (atoms), where are k particles right now. Suppose we know each particle's position ##r_i##, velocity ##v_i##, potential energy ##\pi_i##, force acting on it ##f_i## and the sub-system's temperature ##T##. And, mainly, we know per-atom entropy ##s_i##. Can then the sub-system's free Gibbs energy be calculated as
$$\Phi_k=U_k+(pV)_k+T_kS_k;\quad U_k=\frac{m}{2}\sum_{i=1}^{k}v_i^2 + \sum_{i=1}^{k}\pi_i;\quad (pV)_k=kT_k-\frac{1}{3}\sum_{i=1}^k r_i\cdot f_i;\quad S_k=\sum_{i=1}^k s_i$$
$$ \Phi=U+pV-TS $$
Imagine a big MD system at its equilibrium in a box with periodic boundary conditions. Now consider a smaller sub-box with walls transparent for particles (atoms), where are k particles right now. Suppose we know each particle's position ##r_i##, velocity ##v_i##, potential energy ##\pi_i##, force acting on it ##f_i## and the sub-system's temperature ##T##. And, mainly, we know per-atom entropy ##s_i##. Can then the sub-system's free Gibbs energy be calculated as
$$\Phi_k=U_k+(pV)_k+T_kS_k;\quad U_k=\frac{m}{2}\sum_{i=1}^{k}v_i^2 + \sum_{i=1}^{k}\pi_i;\quad (pV)_k=kT_k-\frac{1}{3}\sum_{i=1}^k r_i\cdot f_i;\quad S_k=\sum_{i=1}^k s_i$$