docs: Update docs in docs/src/Collections.md

Add formula to `PoirierTarantola3rd`
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docs/src/Collections.md

@@ -115,35 +115,41 @@ The $E(V)$ relation of equations of state are listed as below:
 
 1. `Murnaghan`:
    ```math
-   E(V) = E_{0}+K_{0} V_{0}\left[\frac{1}{K_{0}^{\prime}\left(K_{0}^{\prime}-1\right)}\left(\frac{V}{V_{0}}\right)^{1-K_{0}^{\prime}}+\frac{1}{K_{0}^{\prime}} \frac{V}{V_{0}}-\frac{1}{K_{0}^{\prime}-1}\right]
+   E(V) = E_{0}+K_{0} V_{0}\left[\frac{1}{K_{0}^{\prime}\left(K_{0}^{\prime}-1\right)}\left(\frac{V}{V_{0}}\right)^{1-K_{0}^{\prime}}+\frac{1}{K_{0}^{\prime}} \frac{V}{V_{0}}-\frac{1}{K_{0}^{\prime}-1}\right].
    ```
 
 2. `BirchMurnaghan2nd`:
 
    ```math
-   E(V) = E_{0} + \frac{9}{8} B_{0} V_{0} \left(\left( V / V_0 \right)^{-2 / 3}-1\right)^{2}
+   E(V) = E_{0} + \frac{9}{8} B_{0} V_{0} \left(\left( V / V_0 \right)^{-2 / 3}-1\right)^{2}.
    ```
 
 3. `BirchMurnaghan3rd`:
 
    ```math
-   E(V) = E_{0}+\frac{9}{16} V_{0} B_{0} \frac{\left(x^{2 / 3}-1\right)^{2}}{x^{7 / 3}}\left\{x^{1 / 3}\left(B_{0}^{\prime}-4\right)-x\left(B_{0}^{\prime}-6\right)\right\}
+   E(V) = E_{0}+\frac{9}{16} V_{0} B_{0} \frac{\left(x^{2 / 3}-1\right)^{2}}{x^{7 / 3}}\left\{x^{1 / 3}\left(B_{0}^{\prime}-4\right)-x\left(B_{0}^{\prime}-6\right)\right\}.
    ```
 
    where ``x = V / V_0``, and ``f = \frac{ 1 }{ 2 } \bigg[ \bigg( \frac{ V_0 }{ V } \bigg)^{2/3} - 1 \bigg]``.
 
 4. `BirchMurnaghan4th`:
 
    ```math
-   E(V) = E_{0}+\frac{3}{8} V_{0} B_{0} f^{2}\left[\left(9 H-63 B_{0}^{\prime}+143\right) f^{2}+12\left(B_{0}^{\prime}-4\right) f+12\right]
+   E(V) = E_{0}+\frac{3}{8} V_{0} B_{0} f^{2}\left[\left(9 H-63 B_{0}^{\prime}+143\right) f^{2}+12\left(B_{0}^{\prime}-4\right) f+12\right].
    ```
 
    where ``H = B_0 B_0'' + (B_0')^2``.
 
 5. `PoirierTarantola2nd`:
 
    ```math
-   E(V) = E_{0}+\frac{1}{2} B_{0} V_{0} \ln ^{2} x
+   E(V) = E_{0}+\frac{1}{2} B_{0} V_{0} \ln ^{2} x.
+   ```
+
+6. `PoirierTarantola3rd`:
+
+   ```math
+   E(V) = E_{0}+\frac{1}{6} B_{0} V_{0} \ln ^{2} x\left[\left(B_{0}^{\prime}+2\right) \ln x+3\right].
    ```