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VDW_A1 = [real]
Default: VDW_A1 = 1.0
Description: VDW_A1 defines the damping function parameter [math]\displaystyle{ a_{1} }[/math].
VDW_A1 sets the damping function parameter [math]\displaystyle{ a_{1} }[/math] in the DFT-D3 and DFT-D4 methods.