#### Title

Translationally transformed coupled-cluster theory in a local basis for periodic systems

#### Poster Number

11

#### Introduction

There are a lot of interesting problems in surface chemistry where quantum chemistry could give great insight like reaction mechanisms in catalysis, the effect of surface functionalization on semiconductors or the influence of defects on the reactivity of crystal’s surfaces. Coupled cluster (CC) can give an accurate description of bond cleavage and dispersion forces. Unfortunately, the high computational cost of this method makes it impossible to use it routinely on this kind of chemical systems.

#### Purpose

A new approach based on coupled-cluster (CC) theory is proposed. This scheme reformulates the electronic amplitudes to incorporate the periodicity of crystals *and* the locality of electronic interaction. This avoids the calculation of redundant amplitudes. Perfectly periodic surfaces are envisioned as reference wavefunctions for localized defects and chemical reactions.

#### Method

The set of equations was derived algebraically, first, by transforming the final equations of conventional coupled cluster into an infinite form, which contains several infinities that refer to the spacing between atoms. This infinite form accounts for all the possible amplitudes of the system. Next, we restricted the infinities by setting up a radius that discards numerically insignificant amplitudes. This truncation determines a domain of nonzero amplitudes, which can be computed by using set theory. A program was written that generated the necessary code to run the equations. All programs were coded on a 64 core SuperMicro computer on Python 3.6 and C.

#### Results

A set of programmable equations was derived algebraically for the proposed method. Several programs were written to handle this new set of terms and avoid human error. A program was written to generate the transformed equations from the conventional coupled cluster equations. Another program was written generate the necessary code to run the equations.

#### Significance

These new set of equations are the staring point to simulate infinite periodical chemical systems and at the same time describing local phenomena such as bond cleavage accurately. Furthermore, the equations can be improved systematically. The complete scheme could be used to simulate unreachable chemical systems by the current methods, in order to create new semiconductors, understand reaction mechanisms and improve catalytic activity on crystal surfaces.

#### Location

DeRosa University Center

#### Format

Poster Presentation

#### Poster Session

Afternoon

Translationally transformed coupled-cluster theory in a local basis for periodic systems

DeRosa University Center

There are a lot of interesting problems in surface chemistry where quantum chemistry could give great insight like reaction mechanisms in catalysis, the effect of surface functionalization on semiconductors or the influence of defects on the reactivity of crystal’s surfaces. Coupled cluster (CC) can give an accurate description of bond cleavage and dispersion forces. Unfortunately, the high computational cost of this method makes it impossible to use it routinely on this kind of chemical systems.