In addition to Chris' OTFG document, some more description of the
OTF string

2|3.1|4.0|2.2|2|3|5|50U3.4:60U3.1:51:52U3.1{6s1.45,5d0.05}(qc=3)[]

Quantities in <> are descriptions not literals.  All chars outside <>
are literal

<Local cpt>|<r_c(loc)>|<r_c(nonloc)>|<rinner/rcore>|<COARSE>|<MEDIUM>|<FINE>|
   <proj1>:<proj2>...<projn>{<config>}(flags)[<test config>]

Local cpt     :  0,1,2 for s,p,d
r_c(loc)      :  pseudisation radius for local component (atomic units)
r_c(nl)       :  pseudisation radius for nonlocal components (atomic units)
                 (can be overridden as part of projector description)
rinner/rcore  :  Pseudisation radius for augmentation functions and pseudo-core charge
COARSE/MEDIUM/FINE : Recommended cutoff energies in atomic units (Hartree)
projn         : Descriptions of projectors to include, separated by semicolons.

   Syntax of a projector is in it's briefest form

   <n><l>     	  where digits <n> and <l> denote the atomic quantum numbers eg 30 for 3s
              	  In fact this is equivalent to the expanded form "<n><l>UU" where the
              	  projector flags "UU" mean include two ultrasoft beta projectors for
              	  this channel.

   The full form is    
        <n><l>[<type>[<r_c>]][+/-<dE_use>][@<shift>] 
   where anything in brackets  [] is optional (here only).

         <type> can be
         U        - a single ultrasoft projector
         UU       - Two ultrasoft projectors
         N        - a single norm-conserving projector
         L        - use this projector as the local component
	 G        - an ultrasoft GIPAW Gamma projector
         H        - an norm-conserving GIPAW Gamma projector 
         P        - Dummy: do not make a projector.
         LG       - Make Gammas for local channel (not done by default)

         <r_c>    - the projector specific pseudisation radius.
         <dE_use> - the reference energy for the projector. A floating-point
                    value beginning with an explicit '=', '+' or '-' in Hartree.
                    '=E' means absolute energy, '+/-E' is relative to AE eigenvalue.
         <shift>  - Add this value to the projector, it shift it in energy. 

config        : Reference configuration used to generate pseudopotential
                specified in obvious way, eg {3s1,3d0.5}. It is not necessary to
                explicitly mention all core states - CASTEP figures this out.
flags         : Options controlling the type of pseudisation applied and parameters.
                Syntax (flag1,flag2,   ) allows multiple, comma separated flags

   qc=<val>     The optmisation parameter - KE for q < qc is minimised in optimised
                projector scheme.  Can also write (qc=3,qc1=3.5) to specify
                angular momentum channel-specific value of qc.
   tm           Troullier-Martins pseudosation scheme
   pn           polynomial fit
   pb           bessel fit
   es           "extra soft" scheme
   esr=val      extra-soft with explicit specification of r_c
   nonlcc       Do not generate of unscreen with a pseudo-core charge.
   schro        Use non-relativistic schroedinger equation for AE calculation
                 (default is scalar relativistic eqn)
   aug          Explicitly turn on augmentation charges
   scpsp        Generate a self-consistent pseudopotential

test config   : Specify a non-default test configuration eg, [4s1.5,3d0.5].