The difference between order parameter and state parameter?

In summary, the conversation discusses the role of state parameters and the order parameter in fully describing a system. While the order parameter is considered an external parameter in Landau theory, it is still a thermodynamic variable and can be used to expand the free energy of the system. It is also noted that the order parameter can be a function of other thermodynamic variables. Ultimately, it is determined that the order parameter can be introduced as an independent thermodynamic variable in describing a system.
  • #1
Diracmai
4
0
At first, we need some state parameters(like P/T/V) to fully describe a system. And the order parameter is also a parameter which could describe the property of the system.
However, in the Laudau theory, why it said that order parameter is an external parameter(not a independent variable)? Is there any different between order parameter and state parameters(like P/T/V etc.)?
 
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  • #2
I would say no, as in Landau theory we expand the free energy into a power series in the order parameter. Hence it must be a thermodynamic variable.
 
  • #3
DrDu said:
I would say no, as in Landau theory we expand the free energy into a power series in the order parameter. Hence it must be a thermodynamic variable.
Ok! Actually, I also take the some viewpoint as you. In addition, I have another question.Generally, when we use Laudau phase transition theory, we always choose T and order parameter as free energy's variables. In this condition, it that means we hold other thermodynamic variable as constant and only discuss the relation between order parameter and temperature. In fact, the order parameter can also be the function of other thermodynamic variables.
 
  • #4
Diracmai said:
In fact, the order parameter can also be the function of other thermodynamic variables.
Isn't this trivial? E.g. you can describe a gas in terms of V and T or in terms of p and T, the transformation being P(T,V). So you can always introduce the order parameter as an independent thermodynamic variable.
 

FAQ: The difference between order parameter and state parameter?

What is an order parameter?

An order parameter is a physical quantity that describes the degree of order or organization in a system. It is often used to characterize phase transitions, where the order parameter changes abruptly.

What is a state parameter?

A state parameter is a physical quantity that describes the state of a system, such as temperature, pressure, or density. It is used to define the thermodynamic state of a system and can be used to predict its behavior.

What is the difference between order parameter and state parameter?

The main difference between order parameter and state parameter is that order parameters describe the degree of order in a system, while state parameters describe the state of a system. Order parameters are often used to characterize phase transitions, while state parameters are used to define the thermodynamic state of a system.

Can a single physical quantity be both an order parameter and a state parameter?

Yes, a single physical quantity can be both an order parameter and a state parameter, depending on the context in which it is used. For example, in the Ising model, the magnetization can be considered both an order parameter (describing the degree of magnetic order) and a state parameter (defining the thermodynamic state of the system).

How are order parameters and state parameters used in scientific research?

Order parameters and state parameters are widely used in many areas of science, including physics, chemistry, and biology. They are important tools for understanding the behavior of complex systems and can be used to make predictions and test theories. They are also useful for characterizing and studying phase transitions, which are important phenomena in many scientific fields.

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