Initial composition ------------------- .. contents:: This section describes some available initial coniditions for binary fluid composition :depth: 1 :local: :backlinks: none The value of the following input key determines the choice of initial order parameter :math:`\phi(\mathbf{r}; t=0)` .. code-block:: none phi_initialisation choice The available choices are set out below with other relevant input parameters in each case. Some parameters have default values (where stated) and may be omitted. Uniform composition ^^^^^^^^^^^^^^^^^^^ .. code-block:: none phi_iniitialisation uniform phi0 -1.0 The initial order parameter will be set uniformly at all fluid sites to the specified value :math:`\phi_0`. Spherical droplet ^^^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation drop phi_init_drop_radius 8.0 # default 8.0 lattice units phi_init_drop_amplitude 1.0 # default 1.0 A spherical droplet with radial profile :math:`\phi^\star \tanh (r-r_0)/\xi` is initialised. The drop radius can be set in the input, while the centre is always the centre of the system. The amplitude :math:`\phi^\star` may be positive or negative (the centre of the drop will have :math:`\phi = -\phi^\star`). The interfacial width :math:`\xi` will take on the value determined by the current symmetric free energy parameters. Emulsion droplets ^^^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation emulsion phi_init_emulsion_ndrops 4 phi_init_emulsion_radius 4.0 # radius phi_init_emulsion_d_centre 12.0 # distance between centres > 2R phi_init_emulsion_amplitude 1.0 # phi at drop centres Intended to initialise an array of small quasi-two-dimensional droplets (actually cylinders) in the y-z plane. The input specifies the total number of droplets, their radius, the distance between the centres and the amplitude :math:`\phi^\star` at the centre. Block structure ^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation block This initialises a configuration with flat interfaces at :math:`z = L_z/4` and :math:`z = 3L_z/4`. The interfacial width is that set by the current free energy parameters. More general configurations are available via .. code-block:: none phi_initialisation block_X phi_init_block_dimension 2.0 # Extent in x-direction .. code-block:: none phi_initialisation block_Y phi_init_block_dimension 4.0 # Extent in y-direction .. code-block:: none phi_initialisation block_Z phi_init_block_dimension 10.0 # Extent in x-direction In each case, the block entends either side of the centre of the system by half the input value. The interface profile is :math:`\tanh` with width determined by the current free energy parameters. Layer structure ^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation layer_X # or Y or Z phi_init_layer_size 0.2 # 0 < fraction < 1 Similar to the block initialisation except one specifies a fraction of the extent in the required dimension for the central layer. Single interface ^^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation bath A special case where a single interface is initialised in the system system with normal in the z-direction. This is intended for cases without perioidic boundary conditions (e.g., a box), where this configuration makes sense. Random noise ^^^^^^^^^^^^ .. code-block:: none phi_initialisation spinodal # e.g., for spinodal decomposition phi0 0.0 # mean order parameter noise 0.05 # amplitude random_seed 1234567 # random seed Initialises a uniform field :math:`\phi_0` modulated at each lattice position by a small random component drawn from a uniform distribution. Different random configurations may be generated by changing the seed. This is useful to initiate spinodal decomposition, and mimics the effect of a quench in temperature in a real system. Here we have no temperature. Random patches ^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation patches # random patches phi_init_patch_size 4 # patch size lattice units phi_init_patch_vol 0.1 # volume fraction minority phase random_seed 1234567 # random seed Initialises random patches in order parameter (value) of a characteristic size. The total volume fraction of the minority phase (:math:`\phi = -1`) is also set. Different random configurations can be generated by changing the seed. This is intended to allow spinodal decomposition to start in cases where the composition is far from 50:50. If the simple ``spinodal`` method is used in such a case, diffusive effects may prevent domains forming. The larger initial patches promote effective spinodal decomposition. Composition from file ^^^^^^^^^^^^^^^^^^^^^ .. code-block:: none phi_initialisation from_file An arbitrary order parameter field may be supplied from file of appropriate format. See sections on I/O for details.