Greetings! J. Eric Stone made available an excellent molecular modeling and estimation program called Molgen. For details, see the file below: ftp://ftp.ccl.net/pub/chemistry/software/MS-DOS/molgen/README http://www.ccl.net/cca/software/MS-DOS/molgen/ This program installs and runs with no problem on a 25 MHz IBM PS/1 computer with the WIN3.1 operating system. However, on a Pentium II 60 MHz computer (WIN95), a DELL latitude 700 MHz (WIN98), an IBM Thinkpad 900 MHz (WIN98) and a Gateway E-3400 800 MHz (WIN2000), a runtime 200 error occurs. I have now tracked down that error. You may read about it at the address below. Http://www.merlyn.demon.co.uk/pas-r200.htm#why Molgen.exe, startmop.exe and startamp.exe are all affected. Fortunately, using an EXE patch by Andreas Stiller, the problem may be corrected. This patch may be found at ftp://ftp.heise.de/pub/ct/cts/ctbppat.zip I have used this patch to correct the aforementioned programs, and now molgen runs without a problem on the computers listed above. The program molgen.zip will make it easier for you to install the program. Just unzip it to your hard drive (C:\, D:\, etc.) In your autoexec.bat, add the line SET MOLGENTEMP=C:\MOLGEN or some such path for the temporary files generated. Alternatively, you may assign the user varable molgentemp under system properties in windows. For example, for Windows 2000 go to CONTROL PANEL, then SYSTEM, then ADVANCED, then ENVIRONMENTAL VARIABLES. Under USER VARIABLES, select NEW. Enter molgentemp as the variable name and C:\molgen as the value (for example). The user manuals may be found in the original directory ftp://ftp.ccl.net/pub/chemistry/software/MS-DOS/old-molgen/ Note: startmop.exe does not work with Mopac150, which is a WIN95 program, so don't replace mopac.exe with the Mopac150 executable. I think its great that people like Eric make it possible for poor university professors like me to do quality research! Vaneica Young Associate Professor of Chemistry University of Florida young@chem.ufl.edu