1.. index:: improper_style cvff 2.. index:: improper_style cvff/intel 3.. index:: improper_style cvff/omp 4 5improper_style cvff command 6=========================== 7 8Accelerator Variants: *cvff/intel*, *cvff/omp* 9 10Syntax 11"""""" 12 13.. code-block:: LAMMPS 14 15 improper_style cvff 16 17Examples 18"""""""" 19 20.. code-block:: LAMMPS 21 22 improper_style cvff 23 improper_coeff 1 80.0 -1 4 24 25Description 26""""""""""" 27 28The *cvff* improper style uses the potential 29 30.. math:: 31 32 E = K [1 + d \cos (n \phi) ] 33 34where phi is the improper dihedral angle. 35 36If the 4 atoms in an improper quadruplet (listed in the data file read 37by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then 38the improper dihedral angle is between the plane of I,J,K and the 39plane of J,K,L. Note that because this is effectively a dihedral 40angle, the formula for this improper style is the same as for 41:doc:`dihedral_style harmonic <dihedral_harmonic>`. 42 43Note that defining 4 atoms to interact in this way, does not mean that 44bonds necessarily exist between I-J, J-K, or K-L, as they would in a 45linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an 46improper to be defined between the 4 atoms. 47 48The following coefficients must be defined for each improper type via 49the :doc:`improper_coeff <improper_coeff>` command as in the example 50above, or in the data file or restart files read by the 51:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>` 52commands: 53 54* :math:`K` (energy) 55* :math:`d` (+1 or -1) 56* :math:`n` (0,1,2,3,4,6) 57 58---------- 59 60.. include:: accel_styles.rst 61 62---------- 63 64Restrictions 65"""""""""""" 66 67This improper style can only be used if LAMMPS was built with the 68MOLECULE package. See the :doc:`Build package <Build_package>` doc page 69for more info. 70 71Related commands 72"""""""""""""""" 73 74:doc:`improper_coeff <improper_coeff>` 75 76Default 77""""""" 78 79none 80