Výpočty mezimolekulárních interakcí

Abstract

Predikce vlastnostı ́ a struktury molekula ́rnı ́ch krystalu ̊ (krystalu ̊ skla ́dajı ́cı ́ch se z molekul va ́zany ́ch nekovalentnı ́mi vazbami) z ab-inito vy ́poc ̌tu ̊ je na ́roc ̌ny ́ proble ́m. Vazebne ́ energie takovy ́chto struktur vyz ̌adujı ́pouz ̌itı ́pr ̌esny ́ch ab-initio metod, ktere ́ jsou vy ́poc ̌etne ̌ extre ́mne ̌ na ́roc ̌ne ́. Potencia ́ly, ktere ́ lze nafitovat na ab-initio data nebo jejichz ̌ parametry lze zı 'skat z pr ̌edem vypoc ̌tene ́ matice hus- toty, lze pouz ̌ı ́t k popisu interakcı ́ vzda ́leny ́ch molekul, c ̌ı ́mz ̌ lze snı ́z ̌it na ́roc ̌nost cele ́ho vy ́poc ̌tu. Jednou z metod zame ̌r ̌eny ́ch na popis elektrostaticky ́ch pr ̌ı 'spe ̌vku ̊ je distribuovany ́ multipo ́lovy ́ rozvoj rozva ́de ̌jı ́cı ́ matici hustoty do sfe ́ricky ́ch ten- zoru ̊ kolem ne ̌kolika bodu ̊ na molekule. Vyvinuli jsme program, ktery ́ doka ́z ̌e zı 'skat koeficienty multipo ́love ́ho rozvoje ze dvou ru ̊zny ́ch ko ́du ̊integrujı ́cı ́ch matici hustoty, vypoc ̌ı ́tat elektrostaticke ́ pr ̌ı 'spe ̌vky mezimolekula ́rnı ́ energie a ota ́c ̌et multipo ́lovy ́ rozvoj. Toto lze prove 'st do libovolne ́ho r ̌a ́du. Da ́le studujeme vlast- nosti vypoc ̌ı ́tany ́ch koeficientu ̊ multipo ́love ́ho rozvoje v za ́vislosti na ab-initio metode ̌, ba ́zi matice hustoty a ko ́du, ktery ́ byl pouz ̌it pro...

Prediction of properties and structure of molecular solids (crystals compris- ing molecules bonded by non-covalent interactions) from ab-inito calculation is a challenging problem. Binding energies of such structures require usage of precise ab-initio methods, which are computationally extremely demanding. Potentials which can be fitted on ab-initio data, or whose parameters can be obtained from a precalculated density matrix, can be used to reduce the number of computations by describing interactions of distant molecules. One method aiming to describe electrostatic contributions is distributed multipole expansion, which expands a density matrix into spherical tensors around several points on a molecule. We have developed a program that can obtain coefficients of multipole expansion from two different codes integrating the density matrix, calculate electrostatic contributions to intermolecular energy, and rotate multipole expansion. This can be done up to an arbitrary order of expansion. We study properties of calculated coefficients depending on ab-initio method, basis of the density matrix, and the code that was used for the integration of the density matrix. We test the predic- tion of electrostatic energy on dimer datasets of molecular solids with different physical/chemical properties - methanol,...