1.. index:: angle_style class2 2.. index:: angle_style class2/kk 3.. index:: angle_style class2/omp 4.. index:: angle_style class2/p6 5 6angle_style class2 command 7========================== 8 9Accelerator Variants: *class2/kk*, *class2/omp* 10 11angle_style class2/p6 command 12============================= 13 14Syntax 15"""""" 16 17.. code-block:: LAMMPS 18 19 angle_style class2 20 21Examples 22"""""""" 23 24.. code-block:: LAMMPS 25 26 angle_style class2 27 angle_coeff * 75.0 28 angle_coeff 1 bb 10.5872 1.0119 1.5228 29 angle_coeff * ba 3.6551 24.895 1.0119 1.5228 30 31Description 32""""""""""" 33 34The *class2* angle style uses the potential 35 36.. math:: 37 38 E & = E_a + E_{bb} + E_{ba} \\ 39 E_a & = K_2 (\theta - \theta_0)^2 + K_3 (\theta - \theta_0)^3 + K_4(\theta - \theta_0)^4 \\ 40 E_{bb} & = M (r_{ij} - r_1) (r_{jk} - r_2) \\ 41 E_{ba} & = N_1 (r_{ij} - r_1) (\theta - \theta_0) + N_2(r_{jk} - r_2)(\theta - \theta_0) 42 43where :math:`E_a` is the angle term, :math:`E_{bb}` is a bond-bond 44term, and :math:`E_{ba}` is a bond-angle term. :math:`\theta_0` is 45the equilibrium angle and :math:`r_1` and :math:`r_2` are the 46equilibrium bond lengths. 47 48See :ref:`(Sun) <angle-Sun>` for a description of the COMPASS class2 force field. 49 50Coefficients for the :math:`E_a`, :math:`E_{bb}`, and :math:`E_{ba}` 51formulas must be defined for each angle type via the :doc:`angle_coeff 52<angle_coeff>` command as in the example above, or in the data file or 53restart files read by the :doc:`read_data <read_data>` or 54:doc:`read_restart <read_restart>` commands. 55 56These are the 4 coefficients for the :math:`E_a` formula: 57 58* :math:`\theta_0` (degrees) 59* :math:`K_2` (energy) 60* :math:`K_3` (energy) 61* :math:`K_4` (energy) 62 63:math:`\theta_0` is specified in degrees, but LAMMPS converts it to 64radians internally; hence the various :math:`K` are effectively energy 65per radian\^2 or radian\^3 or radian\^4. 66 67For the :math:`E_{bb}` formula, each line in a :doc:`angle_coeff <angle_coeff>` 68command in the input script lists 4 coefficients, the first of which 69is "bb" to indicate they are BondBond coefficients. In a data file, 70these coefficients should be listed under a "BondBond Coeffs" heading 71and you must leave out the "bb", i.e. only list 3 coefficients after 72the angle type. 73 74* bb 75* :math:`M` (energy/distance\^2) 76* :math:`r_1` (distance) 77* :math:`r_2` (distance) 78 79For the :math:`E_{ba}` formula, each line in a :doc:`angle_coeff <angle_coeff>` 80command in the input script lists 5 coefficients, the first of which 81is "ba" to indicate they are BondAngle coefficients. In a data file, 82these coefficients should be listed under a "BondAngle Coeffs" heading 83and you must leave out the "ba", i.e. only list 4 coefficients after 84the angle type. 85 86* ba 87* :math:`N_1` (energy/distance\^2) 88* :math:`N_2` (energy/distance\^2) 89* :math:`r_1` (distance) 90* :math:`r_2` (distance) 91 92The :math:`\theta_0` value in the :math:`E_{ba}` formula is not specified, 93since it is the same value from the :math:`E_a` formula. 94 95---------- 96 97.. include:: accel_styles.rst 98 99---------- 100 101The *class2/p6* angle style uses the *class2* potential expanded to sixth order: 102 103.. math:: 104 105 E_{a} = K_2\left(\theta - \theta_0\right)^2 + K_3\left(\theta - \theta_0\right)^3 + K_4\left(\theta - \theta_0\right)^4 + K_5\left(\theta - \theta_0\right)^5 + K_6\left(\theta - \theta_0\right)^6 106 107In this expanded term 6 coefficients for the :math:`E_a` formula need to be set: 108 109* :math:`\theta_0` (degrees) 110* :math:`K_2` (energy) 111* :math:`K_3` (energy) 112* :math:`K_4` (energy) 113* :math:`K_5` (energy) 114* :math:`K_6` (energy) 115 116:math:`\theta_0` is specified in degrees, but LAMMPS converts it to 117radians internally; hence the various :math:`K` are effectively energy 118per radian\^2 or radian\^3 or radian\^4 or radian\^5 or radian\^6. 119 120The bond-bond and bond-angle terms remain unchanged. 121 122---------- 123 124Restrictions 125"""""""""""" 126 127This angle style can only be used if LAMMPS was built with the CLASS2 128package. For the *class2/p6* style LAMMPS needs to be built with the 129MOFFF package. See the :doc:`Build package <Build_package>` doc 130page for more info. 131 132Related commands 133"""""""""""""""" 134 135:doc:`angle_coeff <angle_coeff>` 136 137Default 138""""""" 139 140none 141 142---------- 143 144.. _angle-Sun: 145 146**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998). 147