Editing Semi-grand ensembles
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== General Features == | |||
== Canonical | Semi-grand ensembles are used in Monte Carlo simulation of mixtures. | ||
We | |||
In the | In these ensembles the total number of molecules is fixed, but the composition can change. | ||
== Canonical Ensemble: fixed volume, temperature and number(s) of molecules == | |||
We will consider a system with "c" components;. | |||
In the Canonical Ensemble, the differential | |||
equation energy for the [[Helmholtz energy function]] can be written as: | equation energy for the [[Helmholtz energy function]] can be written as: | ||
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*<math> A </math> is the [[Helmholtz energy function]] | *<math> A </math> is the [[Helmholtz energy function]] | ||
*<math> \beta | *<math> \beta \equiv 1/k_B T </math> | ||
*<math> k_B</math> is the [[Boltzmann constant]] | *<math> k_B</math> is the [[Boltzmann constant]] | ||
*<math> T </math> is the absolute | *<math> T </math> is the absolute temperature | ||
*<math> E </math> is the | *<math> E </math> is the internal energy | ||
*<math> p </math> is the | *<math> p </math> is the pressure | ||
*<math> \mu_i </math> is the | *<math> \mu_i </math> is the chemical potential of the species "i" | ||
*<math> N_i </math> is the number of molecules of the species | *<math> N_i </math> is the number of molecules of the species "i" | ||
== Semi-grand ensemble at fixed volume and temperature == | == Semi-grand ensemble at fixed volume and temperature == | ||
Consider now that we | Consider now that we want to consider a system with fixed total number of particles, <math> N </math> | ||
: <math> \left. N = \sum_{i=1}^c N_i \right. </math>; | : <math> \left. N = \sum_{i=1}^c N_i \right. </math>; | ||
but the composition can change, from | but the composition can change, from the thermodynamics we can apply a Legendre's transform [HAVE TO CHECK ACCURACY] | ||
to the differential equation written above in terms of <math> A (T,V,N_1,N_2) </math>. | to the differential equation written above in terms of <math> A (T,V,N_1,N_2) </math>. | ||
# Consider the variable change <math> N_1 \rightarrow N </math> i.e.: <math> \left. N_1 = N- \sum_{i=2}^c N_i \right. </math> | |||
: <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N - \beta \mu_1 \sum_{i=2}^c d N_i + \sum_{i=2}^c \beta \ | : <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N - \beta \mu_1 \sum_{i=2}^c d N_i + \sum_{i=2}^c \beta \mu_2 d N_2; </math> | ||
: <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N + \sum_{i=2}^c \beta (\ | : <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N + \sum_{i=2}^c \beta (\mu_2-\mu_i) d N_i; </math> | ||
Or: | |||
: <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N + \sum_{i=2}^c \beta \mu_{i1} d N_i; </math> | : <math> d \left( \beta A \right) = E d \beta - (\beta p) d V + \beta \mu_1 d N + \sum_{i=2}^c \beta \mu_{i1} d N_i; </math> | ||
where <math> \left. \mu_{i1} \equiv \mu_i - \mu_1 \right. </math>. | where <math> \left. \mu_{i1} \equiv \mu_i - \mu_1 \right. </math>. Now considering the thermodynamical potential: <math> \beta A - \sum_{i=2}^c \left( N_i \beta \mu_{i1} \right) </math> | ||
:<math> d \left[ \beta A - \sum_{i=2}^c ( \beta \mu_{i1} N_i ) \right] = E d \beta - \left( \beta p \right) d V + \beta \mu_{1} d N - | :<math> d \left[ \beta A - \sum_{i=2}^c ( \beta \mu_{i1} N_i ) \right] = E d \beta - \left( \beta p \right) d V + \beta \mu_{1} d N - N_2 d \left( \beta \mu_{21} \right). | ||
</math> | </math> | ||
== Fixed pressure and temperature == | == Fixed pressure and temperature == | ||
In the [[ | In the [[Isothermal-Isobaric ensemble]]: <math> (N_1,N_2, \cdots, N_c, p, T) </math> ensemble we can write: | ||
<math> d (\beta G) = E d \beta + V d (\beta p) + \sum_{i=1}^c \left( \beta \mu_i \right) d N_i </math> | |||
where: | where: | ||
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* <math> G </math> is the [[Gibbs energy function]] | * <math> G </math> is the [[Gibbs energy function]] | ||
== Fixed pressure and temperature: | == Fixed pressure and temperature: Semigrand ensemble == | ||
: | Following the procedure described above we can write: | ||
where the ''new'' | <math> \beta G (\beta,\beta p, N_1, N_2, \cdots N_c ) \rightarrow \beta \Phi (\beta, \beta p, N, \beta \mu_{21}, \cdots, \beta \mu_{c1} ) </math>, | ||
where the ''new'' thermodynamical Potential <math> \beta \Phi </math> is given by: | |||
<math> d (\beta \Phi) = d \left[ \beta G - \sum_{i=2}^c (\beta \mu_{i1} N_i ) \right] = E d \beta + V d (\beta p) + \beta \mu_1 d N | |||
- \sum_{i=2}^c N_i d (\beta \mu_{i1} ). | - \sum_{i=2}^c N_i d (\beta \mu_{i1} ). | ||
</math> | </math> | ||
TO BE CONTINUED ... SOON | |||