The article discusses the use of TLS (Translation, Libration, Screw-rotation) parameters to model anisotropic displacements in macromolecular refinement. TLS parameters allow for the description of collective motions of groups of atoms, reducing the number of parameters needed compared to individual anisotropic displacement parameters (ADPs). This approach is particularly useful when data-to-parameter ratios are low, as is often the case with macromolecules. TLS refinement is implemented in the program REFMAC, which uses fast Fourier transforms to efficiently calculate derivatives of the likelihood function with respect to TLS parameters. This makes TLS refinement fast and suitable for routine use. TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used toThe article discusses the use of TLS (Translation, Libration, Screw-rotation) parameters to model anisotropic displacements in macromolecular refinement. TLS parameters allow for the description of collective motions of groups of atoms, reducing the number of parameters needed compared to individual anisotropic displacement parameters (ADPs). This approach is particularly useful when data-to-parameter ratios are low, as is often the case with macromolecules. TLS refinement is implemented in the program REFMAC, which uses fast Fourier transforms to efficiently calculate derivatives of the likelihood function with respect to TLS parameters. This makes TLS refinement fast and suitable for routine use. TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to model both overall and internal motions. The TLS model includes contributions from the crystal, TLS, internal, and atomic displacement parameters. The TLS parameters are derived from the rigid-body motion of groups of atoms, and can be used to