parrinello pressure coupling method
- 1. Molecular Dynamic: Parrinello Pressure Coupling Method Submitted To – Dr. Sudip Chakraborty Submitted By – Usha 16mslsbf16 M.sc Bioinformatics
- 2. Pressure Coupling: The system can be coupled to a pressure bath as in temperature coupling Weak coupling – Berendsen Pressure Coupling exponential relaxations Extended ensemble coupling – Parrinello Rahman Pressure Coupling oscillatory relaxation
- 3. Berendsen pressure coupling Rescales the coordinates and box vectors at every step Yields a simulation with the correct average pressure Equations of motion are modified with a first order relaxations of P 𝑑𝑃 𝑑𝑡 = 𝑃0 − 𝑃 Ƭ 𝑝 here Ƭ 𝑝 represents pressure coupling time constant
- 4. Parrinello Rahman Pressure Coupling Based on constant NPT ensemble: constant number of particles, pressure, and temperature Volume and shape are allowed to fluctuate Extra degree of freedom added similar to Nose Hoover temperature coupling Useful for studying the stress strain relationship of material
- 5. Parrinello Rahman Pressure Coupling Extra degree of freedom added, similar to Nose-Hoover temperature coupling, the Hamiltonian is extended 𝑑2 𝑟 𝑖 𝑑𝑡2 = 𝐹 𝑖 𝑚 𝑖 - M 𝑑𝑟 𝑖 𝑑𝑡 𝑊−1 determines the strength of coupling and the box can be reformed (𝑊−1)𝑖𝑗 = 4π2 β 𝑖𝑗 3 𝑇2 𝑝 𝐿
- 6. Parrinello Rahman Pressure Coupling In most cases the Parrinello Rahman barostat is coupled with Nose- Hoover thermostat The extended methods are more difficult to program but safe If system is far from equilibrium, it may be best to use weak coupling to reach target pressure and then switch to Parrinello coupling method
- 7. References Parrinello, M., Rahman, A. Polymorphic transitions in single crystals: A new molecular Dynamics method. J. Appl. Phys. 52:7182–7190, 1981. Nose, S., Klein, M. L. Constant pressure molecular dynamics for molecular systems. Mol. Phys. 50:1055–1076, 1983.
- 8. Thankyou