To make a density map from a 2D set of data, the first step is to compute values for the third dimension. (Gnuplot has no facilities for computing these values automatically.) The simplest way is to make a 2D histogram; the plot is divided in small 2D regions, and the z-values are proportional to the number of points inside these regions. The following Python script will make an histogram from a time series of two dihedral angles.
GAMESS-US is a full-featured electronic structure software package with MC-SCF, CC, DFT, and CI wave functions. QM/MM, FMO, solvation, and MD calculations are also possible.
NWChem is an electronic structure package that features MC-SCF, MPn, CC, CI, and DFT methods. Properties, solvation models, QM/MM, and MD simulations are also possible.
PyQuante is an open-source suite of programs for developing quantum chemistry methods. The program is written in the Python programming language, but has many "rate-determining" modules also written in C for speed.
The Computational Chemistry Comparison and Benchmark Database (CCCBDB) contains links to experimental and computational thermochemical data for a selected set of gas-phase atoms and molecules as well as tools for comparing experimental and computational ideal-gas thermochemical properties.
Twice today that question was put to me. I thought I’d take a moment and answer it not just for the two individuals who asked, but for anyone who might be wondering. Below is my recommendation…
M. Vasconcelos, P. Mauriz, E. Albuquerque, E. da Silva, and V. Freire. APPLIED SURFACE SCIENCE, 234 (1-4):
33-37(2004)9th International Conference on Formation of Semiconductor Interfaces
(ICFSI 9), Madrid, SPAIN, SEP 15-19, 2003.