TEXPN — Solvation trapezoidal integration shell growth factor.
The size of the integration quadrature used by Amsol solvation models is dependent upon the total number of atoms. For the purpose of efficiency, small systems need only small grids and large systems need large grids. The actual size of the integration grid, NT, is governed by the formula NT = TONE + TEXPN × (Number of atoms). NT cannot be smaller than 4 (for reliability) or greater than 16 (limit of grid size). At 30 atoms (using the default TONE and TEXPN), the maximum grid size is reached with no further improvements in quadrature size for larger systems. Increasing TONE will uniformly increase the quadrature size for small systems, increasing accuracy and computational time.
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