The double quotes are only necessary if the string is in mixed case.
These are the basic rules that CHARMM uses when opening a file:
1/If the filename is in double quotes, remove the quotes and use the string as is.
2/If there are no quotes, first convert the string to all lower case and try to open the file. If this fails convert the string to all upper case and try again. If this fails, issue error message.
