These parameters control the RRKJ scheme and its variants[40, 16]. We have found that Bessel functions are a natural basis set to expand the pseudo wavefunctions, but generally the optimization proposed by RRKJ does not improve the convergence speed significantly.
Optimization can be switched of if NMAX1 and NMAX2 are set to 0. In all other cases NMAX1 and NMAX2 gives the number of Bessel functions used in the optimization, NMAX1 is used for the first set of parameters in the Description section of the PSCTR file 13.4.11 (usually the NC part) and NMAX2 is used for the second set of parameters (usually the non normconserving part). LCONT controls whether the third derivatives of the pseudowavefunctions are continues at the cutoff radius. This results in a continues first derivative of the pseudopotential at the cutoff radius. QRYD is the allowed energy error in the optimization [10, 16].
NMAX1=0 and NMAX2=0 gives always the best pseudopotentials. Anything else is only for absolute experts.