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Manuscript Title: A Programmable Optimization Environment using the GAMESS-US and MERLIN/MCL packages. Applications on Intermolecular Interaction Energies.
Authors: Fanis G. Kalatzis, Dimitris G. Papageorgiou, Ioannis N. Demetropoulos
Program title: MERGAM
Catalogue identifier: ADYB_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 175(2006)359
Programming language: ANSI C, ANSI Fortran-77.
Computer: The program is designed for machines running the UNIX operating system. It has been tested on the following architectures: IA32 (Linux with gcc/g77 v.3.2.3), AMD64 (Linux with the Portland group compilers v.6.0), SUN64 (SunOS 5.8 with the Sun Workshop compilers v.5.2) and SGI64 (IRIX 6.5 with the MIPSpro compilers v.7.4).
Operating system: UNIX.
RAM: Memory requirements mainly depend on the selection of a GAMESS-US basis set and the number of atoms.
Word size: 32 bits
Keywords: Merlin, MCL, GAMESS-US, geometry optimization strategies, basis set superposition error, intermolecular interaction energies, ab-initio potential energy scans.
PACS: 31.15.-p, 31.50.-x, 02.60.Pn.
Classification: 16.1, 4.9.

Nature of problem:
Multidimensional geometry optimization is of great importance in any ab-initio calculation since it usually is one of the most cpu-intensive tasks, especially on large molecular systems. For example, the geometric and energetic description of van der Waals and weakly bound H-bonded complexes requires the construction of related important portions of the multidimensional intermolecular potential energy surface (IPES). So the various held views about the nature of these bonds can be quantitatively tested.

Solution method:
The Merlin/MCL optimization environment was interconnected with the GAMESS-US package to facilitate geometry optimization in quantum chemistry problems. The important portions of the IPES require the capability to program optimization strategies. The 4 Merlin/MCL environment was used for the implementation of such strategies. In this work, a CP-corrected geometry optimization was performed on the HF-H2O complex and an MCL program was developed to study portions of the potential energy surface of the C6H6-H2O complex.

The Merlin optimization environment and the GAMESS-US package must be installed. The MERGAM interface requires GAMESS-US input files that have been constructed in Cartesian coordinates. This restriction occurs from a designtime requirement to not allow reorientation of atomic coordinates; this rule holds always true when applying the COORD=UNIQUE keyword in a GAMESS-US input file.

Running time:
It depends on the size of the molecular system, the size of the basis set and the method of electron correlation. Execution of the test run took approximately 5 minutes on a 2.8GHz Intel Pentium CPU.