This clinical trial aims to compare the efficacy and safety of transcranial Alternating current stimulation (tACS) vs. transcranial Direct current stimulation (tDCS) vs. sham stimulation in chronic schizophrenia. The main question it aims to answer is: • In comparison to tDCS, can tACS improve the clinical outcome of patients with chronic schizophrenia? Participants will be randomised into 3 groups receiving either tDCS, tACS or sham stimulation and changes in psychopathology and neuro-cognition with the interventions will be compared within and between the groups. The primary outcome measure is the Positive and Negative Syndrome Scale (PANSS), while secondary outcome measures are the Auditory Hallucination Rating Scale (AHRS), Brief Cognitive Assessment Tool for Schizophrenia (B-CATS), and Global Assessment of Functioning (GAF).