I am using ViewerLite version 5.0. I want to add hydrogen to a specific site in the crystal structure of vivianite. But the program allows me to add hydrogen in different sites than required. Moreover, the 'add hydrogen tab' is 'off' for specific sites in the structure. So I need details about restrictions and/or limitations of using this 'add hydrogen' command.

Any suggestions would be great. Thanks for your time and help.

Regards,
valliyappan