The three-dimensional structure of humic substances and soil ...

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ergy of the molecular system was calculated with
6993.92 kJ 0.1 nm -1 mo1-1 and a gradient (derivative of
the energy with respect to all Cartesian coordinates) of
91.16 kJ 0.1 nm -1 mol -I. The termination conditions
for this calculation were 83.80 kJ nm- 1 mol - 1 and 11070
cycles maximum. After approximately 4700 calculation
Fig. 6. First approximation (1 cycle, 3 points, convergence limit of
83.80 kJ 0.1 nm -1 mol ~) for the geometrical optimization of the HA
structure (II) given in Fig. 5 (Compute; Single Point; Geometry Optimi-
zation) by semi-empirical calculations. Display of the structure in the
disks mode (Rendering; Disks)
~ J
Fig. 7. Geometry optimization
and energy minimization of the
3 D structure of HA (II, Fig. 6)
after 4700 calculation cycles and
a resulting total energy of
710.70 kJ nm -1 mo1-1 and a
convergence gradient of
0.037 kJ nm- 1 mol- 1
cycles with a convergence limit of 0.83 kJ 0.1 nm -1
tool-l, the energy minimization leads to a molecular en-
ergy of 752.57kJ 0.1 nm -1 tool -1 with a gradient of
0.71 kJ 0.1 nm -1 tool -1. As an illustration of the energy
minimization process in Fig. 7 the corresponding HA
structure is displayed. Rotation of the energy-minimized