add documentation for multidimensional hindered rotors

documentation/source/users/arkane/input.rst

@@ -421,6 +421,44 @@ for specifying the same ``rotors`` entry are commented out)::
 
 Note that the atom labels identified within the rotor section should correspond to the indicated geometry.
 
+Multidimensional Hindered Rotors
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+For multidimensional hindered rotors, ``geometry``, ``frequencies``need to be specified in the same way described in detail in the last section. However,
+rotor files may specified by either a 1D rotor scan file as in the last section (1D rotors only) or as a directory. 
+The directory must contain a list of energy files in the format ``something_name_rotorAngle1_rotorAngle2_rotorAngle3(...).log``.  
+
+For HinderedRotor2D (Quantum Mechanical 2D using Q2DTor):  
+======================= ==================================== 
+Parameter               Description
+======================= ====================================
+``scandir``             file or directory containing scan energies
+``pivots1``             The indices of the atoms in the first rotor torsional bond
+``top1``                The indices of all atoms on one side of the first torsional bond (including the pivot atom)
+``symmetry1``           The symmetry number of the first rotor 
+``pivots2``             The indices of the atoms in the second rotor torsional bond
+``top2``                The indices of all atoms on one side of the second torsional bond (including the pivot atom)
+``symmetry2``           The symmetry number of the second rotor 
+``symmetry``            Q2DTor simplifying symmetry code, default is ``none``
+======================= =================================== 
+
+For HinderedRotorClassicalND (Classical and Semiclassical ND rotors):  
+======================= ====================================
+Parameter               Description
+======================= ====================================
+``scandir``             file or directory containing scan energies
+``pivots``              The list of the indices of the atoms in each rotor torsional bond
+``tops``                The list of the indices of all atoms on one side of each torsional bond (including the pivot atom)
+``sigmas``              The list of symmetry numbers for each torsional bond 
+``semiclassical``       Indicates whether to use the semiclassical rotor correction (highly recommended)
+======================= ====================================
+
+The inputs are mostly the same as the last section except that HinderedRotorClassicalND takes lists of pivots,
+tops and sigmas instead of individual values. These rotors enable calculation of partition functions for 
+multidimensional torsions. It is worth noting that HinderedRotor2D can take on the order of hours to run. To mitigate this the 
+.evals file in the directories Q2DTor directories are searched for automatically and used if present to reduce runtime to seconds. 
+This means if you have run a system with HinderedRotor2D and wish to rerun the system and recalculate the HinderedRotor2D
+ you should delete the .evals file. HinderedRotorClassicalND usually runs quickly for lower dimensional torsions. 
+
 Additional parameters for pressure dependent networks
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~