Constructing Electrostatic Potential Mapping for Molecules and Periodic surfaces

Hi,

I am having difficulty constructing electrostatic potential surfaces for organic molecules (ethanol).

The mappings I construct is shown below. It is quite different from that shown on the web or in the textbooks.

Please provide an expert opinion as to how I can modify this in MS 4.0. I want my surface to be continuous as in the one shown in the textbook.

Best Regrads,
TChen

Electrostatic_Potential_Ethanol.jpg