CH4: Analytic second derivatives

Sample directory: adf/e_CH4_SecDeriv/

The CH₄ example for the analytic second derivatives is very similar to the CN example. The comments are therefore restricted to a few statement.s.

$ADFBIN/adf << eor
title CH4

Define
 ZERO = 0.0
 RCH = 1.0850
 X1 = ZERO
 Y1 = ZERO
 Z1 = ZERO
 X2 = sqrt(3)*(RCH/3)
 Y2 = -sqrt(3)*(RCH/3)
 Z2 = sqrt(3)*(RCH/3)
 X3 = sqrt(3)*(RCH/3)
 Y3 = sqrt(3)*(RCH/3)
 Z3 = -sqrt(3)*(RCH/3)
 X4 = -sqrt(3)*(RCH/3)
 Y4 = sqrt(3)*(RCH/3)
 Z4 = sqrt(3)*(RCH/3)
 X5 = -sqrt(3)*(RCH/3)
 Y5 = -sqrt(3)*(RCH/3)
 Z5 = -sqrt(3)*(RCH/3)
End

Atoms
 1. C X1 Y1 Z1
 2. H X2 Y2 Z2
 3. H X3 Y3 Z3
 4. H X4 Y4 Z4
 5. H X5 Y5 Z5
End

Basis
 Type TZP
 Core None
End

XC
 LDA Xonly
End

integration 4.0

symmetry NOSYM

End input
eor

This time more output is given in the SD part. The input now specifies that 1 iteration is to be done in the coupled-perturbed Kohn-Sham equations before the Hessian is printed. More iterations given a better converged result for the Hessian, but at the cost of increased computer time, which is roughly proportional to the number of iterations.

$ADFBIN/sd << eor
print timing
SD
 CALC GRADIENT HESSIAN DIPOLE
 MAX_CPKS_ITERATIONS 8
 CHECK_CPKS_FROM_ITERATION 1
 U1_ACCURACY 0.0001
END
eor