The following visualization tools are enabled in EDA2:
Automated generation of complementary occupied-virtual pairs (COVP)
Electron density difference (EDD) maps between intermediate states (FRZPOL, POLFull)
Plots for Natural Orbitals for Chemical Valence (NOCV)
As introduced in Sec. 13.5.2, the COVPs can help elucidate the details of a charge-transfer process by showing the chemically most relevant donor-acceptor orbitals. In its implementation in EDA2, we enabled an automated selection of the most significant occupied-virtual pairs (based on a threshold on singular values). The MO cube files of these selected COVPs are then generated, and thus there is no need to specify which orbitals to plot. This new feature can be turned on by setting EDA_COVP_PRINT = 2. Also, both the old and new formats of the $plots section are supported for automated COVP cube generation in EDA2. The old format requires MAKE_CUBE_FILES = TRUE and the new format requires PLOTS = TRUE.
EDA2 also enabled electron density difference (EDD) plots to show the redistribution of electron density upon polarization () and charge transfer (). Another related quantity that can be visualized is the so-called natural orbitals for chemical valence (NOCV), 641 which are defined as the eigenvectors of . The NOCVs appear in pairs and , whose associated eigenvalues are and , respectively. The energy lowering associated with each pair of NOCVs can be calculated using the extended transition state (ETS) approach (see ref. 641 for details). The NOCVs are useful tools for illustrating the underlying orbital interactions in chemical bonding.
In EDA2, the EDD maps are plotted when EDA_PLOT_DIFF_DEN = TRUE. The calculation of NOCVs can be turned on by EDA_NOCV = TRUE, and the most significant NOCVs are automatically selected based on a threshold on the eigenvalues and then plotted. Note that the new format of the $plots section is required for these visualizations.
$molecule 0 1 -- 0 1 O -1.521720 0.129941 0.000000 H -1.924536 -0.737533 0.000000 H -0.571766 -0.039961 0.000000 -- 0 1 O 1.362840 -0.099704 0.000000 H 1.727645 0.357101 -0.759281 H 1.727645 0.357101 0.759281 $end $rem JOBTYPE EDA METHOD B3LYP BASIS 6-31+G(d) SYMMETRY FALSE SYM_IGNORE FALSE MEM_TOTAL 8000 MEM_STATIC 2000 BASIS_LIN_DEP_THRESH 6 THRESH 14 SCF_CONVERGENCE 8 MAXSCF 200 EDA_COVP TRUE EDA_PRINT_COVP 2 !auto-generation of covp cube files MAKE_CUBE_FILES TRUE PLOTS TRUE !new format for the plot section $end $plots grid_points 100 100 100 $end
$molecule 0 1 -- 0 1 N 0.0000001517 0.7279666667 0.0000000000 H 0.9488005016 1.0881357449 0.0000000000 H -0.4743994984 1.0881371276 -0.8216800000 H -0.4743994984 1.0881371276 0.8216800000 -- 0 1 B -0.0000014567 -0.9275533333 0.0000000000 H -1.1719117610 -1.2408021948 0.0000000000 H 0.5859582390 -1.2408039026 -1.0149100000 H 0.5859582390 -1.2408039026 1.0149100000 $end $rem JOBTYPE eda EDA2 2 !ALMO-POL METHOD b3lyp BASIS 6-31g(d) SCF_ALGORITHM diis XC_GRID 1 SCF_CONVERGENCE 8 MAX_SCF_CYCLES 200 THRESH 14 SYMMETRY false SYM_IGNORE true EDA_PLOT_DIFF_DEN TRUE !plot EDD maps EDA_NOCV TRUE !plot NOCVs $end $plots grid_points 100 100 100 $end