Optogenetic inhibition of excitatory subpopulations of the hippocampus has been suggested as a new approach in the treatment of temporal lobe epilepsy (TLE), one of the most common types of drug-resistant epilepsy. While this approach is promising, its application in animal models has proven to be a challenge. This can be attributed to the numerous parameters involved in both the optogenetic stimulation setup and the neuronal environment. These are difficult to investigate and optimize in limited in vivo experiments. Therefore, an in silico approach was developed by refitting the double two-state opsin model (22OM) introduced in Schoeters et al. (2021) to the chloride conducting opsin GtACR2. The resulting mathematical description of the photocurrent was added to all compartments of a slightly adjusted version of the reduced-morphology model of a rat CA1 pyramidal neuron described in Tomko et al. (2021). To investigate the influence of the opsin’s conduction ion type, an option was added to link the photocurrent to either K$^+$ or Cl$^-$ concentrations. The final model, schematized in figure 1A, was used to investigate the effect of the stimulation parameters light intensity (I), pulse repetition period (prp) and duty cycle (dc) as well as the initial K$^+$ and Cl$^-$ concentrations and the conductance ($\rm g_{max}$) and ion type of the opsin on the effectiveness of the optogenetic inhibition of the somatic activity of a with current clamp stimulated CA1 neuron. The results indicate that both K$^+$ and Cl$^-$ are capable of silencing the CA1 pyramidal neuron’s activity but, as shown in figure 1B, that Cl$^-$ photocurrents can be excitatory when (seizure induced) irregular concentrations occur. Furthermore, high intensity stimulation with long pulses in quick succession to each other on an opsin with high conductance is more likely to result in complete silencing. In order to assess the reliance of the above observations on the opsin model, a simplified model (22OMs) is proposed that permits direct access to the parameters describing the photocurrent’s opening and closing dynamics. As illustrated in figure C, varying these time constants can influence the results of the stimulation but the influence of the other parameters remains the same. This indicates that any uncertainty introduced in the modelling of the opsin behaviour does not significantly impact the results and suggests that this simplification of the opsin model in future studies is justified.