Hi, I am interested on calculating the electrostatic potential of a molecular surface on a protein (specifically visualizing that potential on a previously cavity determined by CASTp). However, althought I did get reasonable results using Coulombic potential, I could not obtain similar results using APBS potential (I obtained a surface too electrostatic, charged negatively and the values have a huge range, not only from -10 to 10 as in the case of Coulombic potential). Should I modify some default values out of the calculation parameters in order to get a similar result to that obtain by Coulombic potential? And it is absolutely indispensable add hydrogens in an APBS estimation? Thanks in advance for your help. Best regards, *Andrés Felipe Vásquez J., BSc, MSc.* Grupo de Fisiología Molecular Subdirección de Investigación Científica y Tecnológica Dirección de Investigación en Salud Pública Instituto Nacional de Salud Avenida calle 26 No. 51-20 - Zona 6 CAN +57 (1) 2207700 ext. 1419 Bogotá, D.C., Colombia