Electron Smearing in DFT Calculations: A Case Study of Doxorubicin Interaction with Single-Walled Carbon Nanotubes

To address the choice of an appropriate value of electron smearing to facilitate self-consistent field (SCF) convergence, we studied the interaction of doxorubicin with short armchair and zigzag single-walled carbon nanotube models with closed caps, at the PWC/DNP level of density functional theory. By gradually reducing the electron smearing value from a large and most commonly used one of 0.005 Ha to zero (Fermi occupation), we monitored the changes in close contacts between the interacting species, total energy of the molecular system, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy and isosurfaces, HOMO-LUMO gap energy, and plots of electrostatic potential. It became evident that the commonly used smearing values of >= 0.001 Ha can alter the results significantly (for example, by one order of magnitude for HOMO-LUMO gap energy). We suggest the setting of electron smearing value at 0.0001 Ha, which does not imply too high computation cost and can guarantee the results close to the ones obtained with Fermi occupation. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4197-4205, 2011