Hi, I am using the H-bond function in UCSF Chimera and I noted that the relaxed parameter for angle criteria is 20 by default. However, since that I have no hydrogen atoms in the pdb structure, I assume that the angle theta (donor-hydrogen-acceptor) cannot be used by Chimera as an angle criteria, and so the psi or phi angles might be used instead. Which angle is actually used in the relaxed parameters? And most important, what is the default value of that angle (angle minus relaxing value)? 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